First you must know what you want to draw. In my case I had to draw a peace poster. Then you look at some designs on different sites where different people won on that topic. Study how they won and what designs they used. Study it for about 2 minutes then go in a quiet room and take about 2-5 minutes to think of what you want to join. If you want you can combine what the other winner did to what you want to do. Then you take a scratch piece of paper and sketch out what you think.
It took me 20 minutes to draw what I wanted to draw and carefully examine it. It might take you less time but I would recommend that you take 20 minutes to draw and carefully examine it. You always have to look at it first before you draw it because if you make any mistake if you didn't draw it out first it will be hard for it to look exactly as you planned it would be. When you are done sketching it out, do it 2 more times. When you feel that you have mastered it then do it for real! When you are done turn it in. With those steps you will win!