Building on Lark's input. Not only is anger unstable, but in using it in magic, it can take positive spells, and turn them negative(ie instead of a protection spell, you'll attract bad luck.
My go to solution is of course meditation. If you can't control your anger than you should not be doing magic, you'll only put yourself in danger. If you can learn to control it and focus on positivity, it will greatly improve your workings because strength of mind will lead to greater focus of will and increase in your ability to focus your energy.
If you don't know how to meditate there are several very informative threads that can guide you through the process.