You really do need to get well informed.
You can easily read a chapter in a good book about sealing and insulating attics before starting an DIY insulation installation. Check Very Helpful Books.
Insulation.com recommends Insulate and Weatherize by Bruce Hartley. Cut your Energy Bills Now is also very good.
Both books have extensive sections on air sealing an attic with many useful drawings and photographs.

A good place to start is ...

Download the well-prepared Do It Yourself Guide to Sealing and Insulating produced by the U.S. Department of Energy.
The guide is an excellent overview. And, you will need to learn more to do a safe, economical, and energy efficient DIY attic insulation installation.

Safety issues are big

Ignorance can be dangerous and expensive.
The wide ranges in home construction and condition, safety issues, and local weather make it essential to get professional guidance before doing a DIY attic insulation installation.
Tell an Energy Auditor you are planning to do a DIY insulation installation in your attic. Ask for specific guidance in doing a safe, energy efficient, and cost effective insulation installation.
Rodent damage to wiring is a major cause of home fires. The Auditor can help you deal with safety issues like the integrity of the electrical system in the attic, hot surfaces like vents and chimneys, unrated electrical fixtures, and insuring there is sufficient combustion ventilation for furnaces, stoves, and water heaters.
Correctly dealing with moisture barrier and attic ventilation issues can prevent the development of major structural problems over time.
You can decide to do some DIY insulation installation tasks, and have others done by an insulation contractor.

Step One: Inspect, document, and organize

Inspecting your attic

You can save money and get the best possible insulation installation by inspecting your attic, reading, and organizing your questions before obtaining the Energy Audit or insulation contractor bids.
Take a flashlight, small digital camera, tape measure, pad and pen, and at least three two-three foot by four-five foot pieces of 5/8 inch plywood platforms for working surfaces. Knee pads are strongly recommended.
Extra lighting can be very helpful. Cheap aluminum reflector dish painter lights on an extension cord can be a big help. They are easy to move as needed, plug into each other, and quickly attach to rafters or joists with large clips.

Locate and inspect all hot vents from stoves, water heaters, bathroom heaters, furnaces, chimneys, etc. Check the vents for gas leaks and stability. Flex pipe may have sagged over time. The vents should not have any down turns or horizontal runs.
Note the depth, type, and consistency of any existing insulation.
Move old insulation as needed to find air holes around plumbing and electrical penetrations, lighting fixtures, seams, duct chases, etc. Dark stains on insulation indicate air leaks.
Note if rodent or bird dropping are present. Check wiring to see if rodents have nibbled it. Confirm that junction boxes are correctly sealed. Check for insect colonies.
Be sure to wear a good respirator mask. Not a regular dust mask. Particularly, if the old insulation is fiberglass. A good choice is the 3M HEPA mask.

Document

Take a lot of photographs. A small digital camera with a flash and telephoto lens will make this easy.
The photos will enable you to better plan work and materials. They will also enable you to accurately communicate when buying materials or getting help.
The gross measurements of the attic are easier to do from within the house than in the attic.
Count all eave, eyebrow, end, and ridge vents and check the condition of the vent screens. If they are old, painted over, or otherwise at the end of their useful life, then replace them before doing your insulation installation.
Note the condition of any attic vent baffles. Do not be surprised if there are none.
Note any signs of old or new moisture on any surface. Any leaks need to be repaired before installing insulation.
Write down your questions and comments as they occur to you.

Organize

Organize your questions after you have done some reading and inspected the attic.
Select the photos that will help you discuss questions and issues.

Issues to bring up with an Energy Auditor or Insulation Contractor.

Ask for a comparison of the cost and energy efficiency of the primary home insulation materials and installation methods that are best for your climate.
Ask about correct and complete air sealing with the right materials and methods to achieve a good thermal barrier for your attic.
Ask about all other major topics including, attic ventilation, moisture barriers, the optimal R-values, and the best choice of home insulation products for your needs and budget.
Ask about specific technical issues like boxing and insulating the attic entry, making and insulating foam board barriers for closing large holes, selecting and installing attic vent baffles, safely boxing light fixtures and hot vents, using non-flammable sealers near hot surfaces, etc.
Ask about the advantages of sharing insulation installation tasks with an insulation contractor.
Your DIY preparation work of air sealing, installing vent baffles, boxing the attic access, etc. may enable a good contractor to do the actual insulation installation for a very attractive price.
Talk to insulation contractors about you doing some tasks and the contractor doing others.
You may learn that more of the important insulation installation projects can be completed with you doing the work you can, and the insulation contractor doing jobs that require specialized equipment and experience such as insulating existing walls.
Get at least three bids from home insulation contractors before starting an attic DIY insulation project.

About the "No Problem" approach to attic insulation.

Some large fiberglass manufacturers rent machines from big box retailers that blow in low-density fluffed fiberglass insulation. They have many "It Is So Easy" videos that seem to fly over many important points.
One major point is that low-density fluffed and blown-in fiberglass is about R-2 per inch. This means you need thirty-two (32) inches of insulation depth to meet the R-60 attic insulation code in many parts of the country (figures are from the Owens Corning AtticCat tm R-Value chart)
Thirty-two (32) inches of depth is a LOT of attic insulation.
Even temperate climates like the central coast of California have a code requirement of R-38 for attics. That is about 19.5 inches of depth for blown-in Owens Corning fiberglass.
The high bulk of low-density fiberglass makes it impossible to install sufficient insulation in some important sections of most attics.
So, low-density fiberglass DIY insulation installations often ends up Far below the code standard that define the energy efficiency needed for effective home insulation installation in your local climate.
It is ignorant and wasteful to not meet or exceed local code standards for home insulation energy efficiency. Falling short will waste a lot of money and energy every month for years to come.
There are other problems with the "no problem" approach.

Selecting insulation materials and installation method

Please read the Home Insulation Products Comparison page for descriptions of common insulation materials.
Blown-in insulation installation is generally better than batts for most attic retrofits.
It is hard to avoid having gaps and compressions with batts, especially in tight, irregular, and hard to reach places. And, it is a Lot more Very hard work.
Blown-in cellulous can easily and completely fill all gaps including irregular and hard to reach areas.
Blown-in cellulous is about R-3.5 per inch, which is almost double the R-2 blown-in fiberglass. You get almost twice as much insulation energy efficiency for many attic areas with limited space.
Cellulous provides pest control for rodents and most insects including some termites. Cellulous also provides better sound dampening and resistance to air leaks.
Cellulous is in the same price range fiberglass. It meets all state and national fire codes.
The quantity of insulation product you need depends on the R-Factor and the square feet of your attic. You can learn the required R-Factor from your Energy Auditor, insulation contractors, or your local building department.
Check the selected home insulation product material package or website for the number of square feet covered per package for each specific R-Value.
In most cases, it makes sense to leave existing insulation in place. Removing it is hard work, and generally a waste of time.
Since old insulation is commonly very uneven and totally insufficient, it is best to calculate the amount of new insulation needed without including any benefit gained from the old insulation.

Step Two: Air Seal and Prepare the Attic

Air sealing and preparing the attic is the hardest and most important part of a good attic insulation installation job.

This is hard and tedious work.
And, it is worth it. If, you get informed and do it right.
Most of the hard work comes before the actual insulation installation.
Careful attic preparation will save a Lot of money and assure your personal safety.

Air sealing

All air and heat leaks have to be effectively sealed or the value of your home insulation installation will be greatly reduced.
Use a professional type of canned spray foam insulation applicator with a nozzle extension for installing low expansion foam.
Seal all cracks, holes, seams, gaps, etc. as you learned to do from reading, the Energy Auditor, and bidding insulation contractors.
Caulking is also useful for smaller cracks, seams, and holes or any place were the expansion of the foam could be a problem.
Look for heat leaks that are not holes. These include thin metal flashing around vents or un-insulated drywall that can allow heat transfer. A surface or insulation that is dirty indicates a heat leak.
If in doubt, seal and insulate it.

Attic Vent baffles

Attic vent baffles are very important.
Correctly installed vent baffles keep wind and moisture from affecting installed insulation and enable essential attic ventilation.
The three common kinds of attic vent baffles are cardboard, pressed foam, and recycled PVC.
All are easy to install with a staple hammer. They can be quickly trimmed to fit any size vent. Care must be taken to be certain that the bottom of the baffle is well fitted and fully secured.
The best attic vent baffles are made from recycled PVC. Cardboard absorbs moisture and will rot over time. Foam is less stable than PVC.
Accuvent (PVC) is a superior vent baffle product that is easy to install, flexible enough to fit well into the bottom of the eve, and allows full insulation depth to the outer edge of the attic. They come in two lengths and are sold at Home Depot and other big box retailers.
Be certain the top of the baffle will be well above the level of your new attic insulation.

Recessed light covers

The best and simplest way to insulate recessed light fixtures is with a fireproof cover.
The covers are very easy to install, and will substantially improve the total energy efficiency of your insulation installation.
Even properly sealed recessed lights can be a significant source of heat loss.
Tenmat produces a good light fixture cover that meets all fire codes.
Some insulating light covers are sold which are not fully rated to meet all fire codes.
It is critical to only use light fixture covers which meet all fire code standards and have been independently rated by a testing laboratory such as UL or ETL.

Boxing hot surfaces

Sheet metal flashing can be used to box a hot surface so there is 3" of clearance from any insulation.
Self-tapping sheet metal screws and metal furnace tape can help build, secure, and seal seams on flashing.
Be certain the flashing is plenty high enough so insulation does not spill over the top during installation or afterwards.
Use a non-flammable sealer around any potentially hot surface.
Repair and secure hot vent pipes as needed. Metal furnace tape can be used around all seams and joints as a precaution that will stop many small leaks and improve stability.

Closing larger openings

Rigid foam board insulation can be cut to fit open areas in knee walls, soffits, duct chases, porch overhangs, dormers, dropped ceilings, etc. Some foam board insulation has a reflective covering that can improve the energy efficiency of the insulation.
Canned spray foam insulation and good quality tape can be used to seal the foam board edges and seams.
Check the DIY Duct Insulation page for recommendations on quality types and brands of tape.
Use insulation or additional layers of foam board to get a sufficient R-Value so the opening is fully insulated.

Install Attic Rulers

Attic rulers are paper strips with depth measurements. They help confirm an adequate and consistent insulation installation.
You can easily make a few of your own paper markers and staple them to vertical surfaces at a measured height so you can be accurate in getting the right insulation installation depth.

Step Three: Insulation Installation

Most of the hard work is already done!

Blowing in attic insulation is a two-person job. One person is in the attic blowing in the insulation. The other person is feeding insulation into the machine.
Rental insulation blowers have a control switch at the end of the hose and are slow enough so the flow of insulation is easy to control.
Start at the far corners and work back to the attic access.
Go slow enough to completely fill all cavities and get a full and even insulation installation.
Check as you go to be certain insulation is not sprayed behind flashings where it can come in contact with hot surfaces.
Avoid doing attic insulation on a hot day.

Summary

Doing attic insulation installation is hard work. And, it is not simple.
A well-informed and careful homeowner can do a good and safe DIY insulation installation.
Good deals can be made with insulation contractors that include a combination of DIY insulation and contractor work.

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