White, the thing that keeps me from overtrading or taking trades that are not set up properly is my trading plan. You must have strict rules that you follow to enter a trade. I keep my entry and exit rules next to my computer and review them from time to time to make sure I do not take a trade unless there is a proper set up.
If you don't keep a trading journal, you should. By going back and reviewing your trades, you will be able to identify when you are overtrading or taking trades that are not set up well. By continually reviewing your mistakes you will learn to eliminate your mistakes.
Also, as was mentioned in previous posts, you should probably have a limit on your maximum loss for a day. If you hit that limit, quit trading for the day.