Step 1: Do you need it?
I DO NOT RECOMMEND DOING THIS IF YOU HAVE ASTHEMA
You're probably reading this because you need to insulate your attic, or would like to add some insulation to your attic. Either way this is a simple cheap way to take care of the problem.
I needed to insulate my attic after moving into a new house that had no insulation whatsoever. I decided to look in the attic because I had the hardest time keeping my house warm. My house was built in the 30's when houses were built without insulation.
I went to the home improvement store and looked at the insulation and decided on blow in insulation because it is recycled, doesn't itch, and is simple to work with. They only had one blower there and someone had it, and I did not want to rent it anyway, nor did I have a way to get it to my house (I drive a Honda Accord).