A lot of good advice here. I'll just add that I think it is important to be self aware. In fact, I think it's really important.

Day trading involves quick decisions. I was just reading another thread that talked about over trading and other things. If a day trader loses his/her 'cool', if often leads to bad trades. So it's important to be aware of your mood etc. This is much more difficult to control than it sounds. Taking a loss is not easy, and then not letting it get to your head is even harder.