Well, first off, After Effects is pretty much used to "finish" off something you have already planned through, to add that special "pizzaz" to what you have.
Storyboard what you want to happen.
Compile the clips (avi files) that you need t "piece" together to make it happen.
the best use of AE that I find is to do transitions (which are better in AE than in premiere), or to place clips on top of one another, or some fancy set-up to make the video interesting.
There are some "samples" you can look through provide by AE and I suggest picking up the Adobe "Classroom in a book" series for After Effects. There are other great books to find at Amazon.com as well.