Some advice
As a fellow AfterEffects user, I've got to say this - the special effects should be dictated by the story, not the other way around. In other words, don't make a tiny movie about nothing whatsoever purely because you want to show some effect you've managed to create. By all means keep learning new effects and testing them out, but it'd be far more creative to come up with a short script that neccesitates the use of special effects, rather than putting them in a 20-second film with no story or dialogue whatsoever.
I know what you've submitted is just a special effects test and I'm perhaps being a little harsh, but if you want real advice then visit any AfterEffects forum on the net and speak to people there, as the NG Portal really isn't the best place to put stuff like this up. I highly recommend searching for 'video copilot' in Google, as this has an excellent forum for AfterEffects advice and techniques, and has several high-quality tutorials.