From a Drysuit Newbie (well, Novermber anyway...)
* Remember to attach the hose before you get in the water. After diving wet for 4 years, I forgot again just last week....
* Be sure the zaipper is really closed. Sometimes it stops right at the end, but isn't really closed-closed. Always give it a little tug.
* Don't go Michelin Man with the thing. Its Exposure protection, not a full-body buoyancy device.
* No cotton - you will sweat and cotton will only make it cooler and really uncomfortable. This means Sox, T shirts, Sweats, etc. No cotton.
* No Wire Hangers. I just like saying that...
* Buy or make a fat bodied hanger and store it with the zipper open. Others will provide links to their dryers and hangers and other mad-scientist devices soon, I'm sure.
* The seals don't need to be TIGHT, the need to be firm. I don't come up with neck hickey rings from my neck seal...and its never leaked. I'm blown away at how many people have it so tight they get marks on their neck (not that that's always a bad thing...but when diving...)
* If you pull it off part way on your SI, be sure to not SIT on your neck seal. On my last dive, one guy sat down in the galley on something and ripped his neck seal.
* You don't need ankle weights. You do not need ankle weights. I don't get that. Why would you put a weight on your motor?
* Practice, Practice, Practice. Practice donning and doffing at home. Best to look like a dork in front of the mirror and not the entire dive boat. My LDS said it'd take about 10 - 12 dives until your feeling comfortable and confident. I was probably close to that before I got to the point where its a no brainer (except for the %#^$& hose...)
There's tons more... be safe and go guppy diving the first few times out. Mike's right - keep it pool-like for the first several dives. Its like Skiing.... "Oh. I'll show you" and a buddy takes you to black diamond death run and says "now, watch me....." and zip - he's gone. If you're not comfortable, or if the conditions (as they are up there often) are real surgey, etc. Its not time to practice and "just watch me." Be careful, as it is quite different from diving wet.
You'll love it, by the way.
K