If you've noticed that your SSF4 ground game is lacking a certain something, or if you realize you're getting crushed by a savvier (or older!) opponent's ground game, then maybe it's time for you to properly learn some footsies.
Majestros has pretty much compiled one of the best, easiest to understand collections of knowledge on the subject of footsies and waging the middle-distance war in a series of 12-some articles, summarized into what he calls the Footsies Handbook. This is practically required reading for anyone that is just getting into Street Fighter, the King of Fighters, or just about any other 2D game where spacing is important -- regardless of what character (or game) they're going to play.
Let's just say that I'm going to be doing a whole lot of reading, experimenting and learning from this.