I think the first place to start would be to make a list of the ways in which the two seasons are the same. Is there something in your life that happens in the spring as well as the fall? What do these two seasons symbolize? Think about what occurs in the spring and the fall in regards to the life cycle; are there any similarities?
Differences are probably going to be a great deal easier than the things they have in common, so I would start with similarities first.