Don't be afraid to break all of the rules and try something totally new and different. Be contrary. Experiment. Go a little crazy. It might go totally wrong, but it might also go really right, and either way you'll probably learn something. (Plus you can use up some ugly or cheap fabric while you're at it.)
Wine and scalpel-style seam rippers don't mix well, even though it might seem like a really good idea at the time.
Your cutting table is not a good spot to paint something, despite all of the lights and the convenient height. (*sigh*)
Keep some "regular" scissors in the sewing room too, for opening packages and other non-fabric cutting tasks. Also to serve as "decoy" scissors, if you live with scissor thieves.
Live in your house YOUR way - don't be afraid to take over the master bedroom or the living room (or both!) for your sewing if that what works for you. (Keeping your cohabitants' needs in mind too, of course)
Cheap is cheap and quality does matter, at least to a certain degree. Don't be shy about passing on fabric or sending stuff back if the quality is not up to par. Otherwise you'll end up with a cupboard full of "bleh" quality fabric that you don't really want to use.
If you buy pre-cuts of any kind, open them and check them as soon as you get them. Otherwise you might open it up a year or two later and discover bad cuts and have no good way to get a replacement for those pieces. If you're buying them at a show or expo, open them before you leave the grounds. You probably want to look at them anyway - this is your excuse!
Close your rotary blade after every cut, every time. FORCE yourself into this habit, you will not regret it! It'll help keep your blood on the inside where it belongs, plus it will help avoid things like bumping the blade into folded up fabric and putting a series of slashes right in the middle of some precious yardage! (I'm still mad at myself for that one.)
Don't try to sew if you're sick. If you're like me, you're just going to do everything wrong and end up feeling worse, because you'll still be sick and now you've got a bunch of seams to rip out and/or fabric to re-cut. Also, sneezing while rotary cutting is pretty terrifying.