BRACKET!

I can't count the number of times I've screwed up a shot by under- or over-exposing it. Take three pictures, one a stop over what your light meter tells you, one spot on, and one a stop below.

And of course, just take lots of pictures. This is easier and cheaper now with digital photography; it used to get quite expensive with film. With digital, you can always delete the bad pictures (and there will be lots of them), but the more pictures you take, the more will be worth keeping, and the better you will get at taking pictures.