Grammar and Spelling - I'd be remiss if I didn't mention grammar and spelling. Do your best to correct typos. And re-read what you typed. Try reading it out loud to yourself, or to someone else. Frames - One of my pet peeves.
Frames can be nice, when used effectively.
And, for beginners, I suggest not using them at all. I tend to agree with Jakob Nielsen, Frames Suck Most of the Time . I'll probably be adding more to this list as I find more and more websites that are carelessly thrown up onto the web.