How Do You Write Short Songs?

With music like ours, I feel like they all sound not similar but a lot of the time it's in the same key and all this stuff. So you could all just get away with starting one track and making four tracks out of it. The acoustic stuff is actually, for some reason, like it starts me to like figure out how to write like three minute songs that are based off of acoustic parts because I don't want to have slow sections really that aren't interesting.