Before you begin, have a plan. Do some rough sketches and layout ideas before you jump head first into your final page. You want to try to solve as many problems as possible to avoid them while they are still easy to fix.
Check your spelling! Have a dictionary or word processor handy if you are not sure. You may also try typing your dialogue into a word processor or other computer program that has a spell-check feature.
Run your ideas by another person. Sometimes a second (or third, or fourth, etc.) outside opinion can shed light on problems you didn't see, or provide suggestions that can make your comic even better. Sometimes you can get so involved in making it, it is easy to miss even the simplest things.
Draw what you draw best. It's much easier and relaxing than struggling with things you haven't tried drawing before. (Then again, it is important to push yourself in order to get better.)
You can make your comic as intricate or as simple as you please, you are the creator of it after all.
And most importantly have fun , its no use trying to make a comic book and not enjoying the process.