I have a Seat of the Pants Fastback full body harness that I find to be very good. It goes on easy, quick and quiet and is a good design for catching and holding you should you actually fall.
When climbing the stick, I just make sure to keep three points on the stick at all times, moving only one hand or foot at a time. On stands that I use frequently, I leave a tether rope in the tree and hook up before stepping into the stand. Otherwise I try to strap up before stepping to the stand. Stepping on and off the stand is when the fall is most likely, so you want to be hooked up then. I ALWAYS use the harness and belt when installing any climbing devices and the stand.
I applaud HSS for making the harness easy to use, but their harness has a major design flaw IMO. Look a the leg straps. They are really crotch straps and can really hurt you. The leg straps need to pull out to the side, not up thru the middle. Pat Lefemine did a harness test over at the Bowsite. It's good reading and I'm sure it's still there.