Lastly, I would invest in post-software such as lightroom 3. It'll help you fix those photos that didn't come out exactly as you hoped and your keeper rate will increase. Plus, it is a tool that every serious photographer should have, so down the road when you get even more serious you will already have it.
My wife just did a shoot the other day, and long story short out of the camera there pretty much wasn't a single usable photo. However, after a few hours in lightroom (and a bit of time in photoshop) we were able to deliver a couple dozen decent photos that the client was very happy with.
On that note, although not necessarily a "best practice", since you're new to it if you have doubts about your ability to frame a shot, take it a little wide and you can always crop. I'm sure I'll catch a lot of flack for suggesting it, but the truth is you can cut out extra but you can not paste in what isn't there.