Make sure that you have the necessary tools ready - tape measure, straightedge, utility knife (with new blades), and a squeeze-type stapler.
Consider having the following items available - a pole for pushing insulation into roof rafters and other hard to reach areas, stepladder, boards (for sitting or standing in attic areas with no floor), portable lighting source.
Wear a long-sleeved shirt, long pants, and work gloves - insulation can irritate bare skin.
Select an insulation of the appropriate thickness to achieve the R-value you want (R-value is a measure of insulation's effectiveness) and that will fit in the available area.
Leave fiberglass insulation in its packaging until you are ready to use it.
Place the insulation between studs, joists, and rafters, stapling into place as you go.
Stuff scraps of insulation in any open areas where heat loss may occur.
Cut insulation as necessary by placing it paper/foil side down and pressing firmly with your straightedge where you want to cut. Use your utility knife to cut the insulation, using the straightedge as a guide.
Go back and caulk any cracks or areas around windows and doors where drafts can get through.