one of the biggest things (and most frequent things) I do is to blow my top over little things. I suffer from migraines, and they tend to put me on a razor's edge as far as my moods go, so I will often yell at my kids for very minor things.
My parents have never once said "I'm sorry" to me in my whole life, and I am determined not to be that way with my kids. So as soon as I calm down I will tell them I am sorry for yelling an explain that it really wasn't their fault, but that I am oversensitive because I don't feel good.
I've also gotten to the point that I can feel myself getting "crabby" - so I will warn them, "I really don't feel good today, so give me some time to myself, because I don't think I'm going to be in a very good mood."
It has really helped a lot.