I would suggest that if you have a character doing some kind of action, that you should chose characters that are actually making some kind of motion.
In fact I'd go as far as to suggest that you pick and choose carefully which toons that you use just as carefully as you might choose your words.
A good cartoon/comic is a gestalt of word and action. Then you can consider the three beat joke. That is, using a three panel cartoon to get your humor across.
One way to start would to be hitting random for your cartoon and then trying to decide what would be funny to others there. But do not spam the forums with your first ideas. While we have all done it, I am sure that we regret the earlier material.
I know that I do.
Regardless, welcome. And be careful. It's a jungle in here.