The Street Fighter IV series combo system is highly movement-oriented. Most characters have rigid juggle flowcharts, which means it usually doesn’t take long to find all their best juggle combos. That doesn’t leave much room for improvement in the air, so we have to focus on the ground for further optimization.
The key to constructing advanced SF4 and SSF4 ground combos is understanding how each attack affects the distance between your character and the opponent. Generally speaking, all attacks are supposed to push the opponent away to prevent combos from becoming infinites. Your task is to find ways to minimize or negate that countermeasure.
The first thing you should look for are attacks that move your character forward automatically. For example, Cody’s F+MP glides ahead during startup and produces frame advantage, essentially eliminating its own pushback. If you can find a way to combo back into any such forward-moving attack, you’ll probably end up with a loop, as SF4 Akuma’s far s.HK proved.
Another method of creating forward movement is to simply walk forward between attacks. For instance, Ken’s s.LP provides +7 frame advantage and connects on the 4th frame, which gives him 3 frames to walk forward between each jab.
Of course, every character can also combo into EX Focus Attack or Focus Attack dash cancel to cover a ton of ground at the cost of two meter bars. Basically SF4′s FADC system allows you to glue together any three meterless ground combos of your choosing.* Thus the emphasis shifts toward optimizing each of those individual pieces.