I'm by no means an expert on this subject, but I've found that the most effective way to reduce file size is to reduce the frame rate. Anywhere from 10 to 15 fps will make for a much smaller size, and the clarity of each frame can be maintained at a higher quality setting. Also, you can try lopping off the highest and lowest audio frequencies altogether. This will make life easier for the audio encoding element and result in smaller files.

There are of course dozens of other techiques and philosophies, but those are two general ones that can help quite a bit.