Wear a respirator and goggles and do it during the coolest period of the year; even so, bring some water with you. Put down as much as you can afford to (as thick as possible, but evenly thick). When my contractor did mine, he put in 1-2 feet thick.
Also, because I live in Phoenix, we installed some ventilators on the roof to help exhaust hot air in the summer (in addition to the peak eave "vents" at the ends of the house). We wanted to do an exhaust fan, but there wasn't any way to get one into the attic. So far, the ventilators have worked fine.
If you've never done it or seen it done before, my only real advice is break up the cellulose into fluff before you put it into the blower machine, and put little bits gradually and slowly rather than stuffing it to the top. My wife thought she could shove a whole bag inside and have the mixing blade break it up, but it clogged the machine instead, and I had to waste a couple of hours unclogging the tube.
In terms of applying the insulation, you just want it to be thick, fluffy and somewhat even.
Other than that, just captain obvious stuff:
- you need two people (one in the attic and one feeding the blower machine)
- start from the edges towards the manhole
- use a respirator mask
- stay hydrated and take breaks if you need to (the attic is surprisingly hot)
The worst mistake I've ever made in an attic was doing cable runs (TV to the bedrooms) on a summer day in Texas. Sure, we started when it was cool at 7am... but we finished around noon.
So, to add to that: do it on a nice day in spring or fall.
Any particular advice/pain points for re-insulating an attic with cellulose?