Stand in front of a mirror to practice your evil stare.
Narrow your eyes and try not to blink. Keep your mouth in a pout and furrow your brow. These aspects of your look should work together to create an intimidating evil stare.
Think about something that angers you. Picture the person or incident in your head while staring. Keep this in the back of your mind every time you do your evil stare.
Keep a straight face. Although it may seem comical at first, you should not laugh while practicing your evil stare. You have to look mean in order for the look to be taken seriously.
Ask friends to tell you whether it's effective or not. Perform several evil stares for your friends and let them decide on your best one.