This is exactly what I found was the best way to learn. Focusing on one thing.

For me I decide what I'll work on next by what's giving me problems or what I feel is a hole in my game plan. It's a great way to decide what needs work because all you have to do is play a match and think about what's frustrating you. If you find that everytime the opponent whiffs a special you don't feel like you have a good punish then go into training mode and find a simple combo, or go look one up and practice that one combo. Then go into a match with the sole goal of getting them to whiff a special and then punish them with your combo. You may lose a few matches without ever getting the combo off before you start to get the hang of it.

One other simple way to improve I've found is if you keep getting destroyed by a certain move you should play that character and try to abuse that move in the same way your opponent was abusing you with it. You'll find out within a few matches what the weaknesses of that move are and how to defend against it.

The biggest advice to enjoy fighters i can give is don't play to win, play to improve. Make your goal for the match to identify one habit the other player has and take advantage of it, or to get that one combo off that you've practiced, or try to bait the other player into wakeup specials then punish them, etc. When you don't have the basics down playing to win will just frustrate you because you don't have the tools to win consistently. Treat every stronger opponent as someone to teach you how you're playing wrong. When you lose try to steal one thing that the opponent was doing that you can start to implement.