I think a few things have contributed to the marked improvement in Muamba's play recently.
1. Natural maturity. Lest we forget, the boy is still only 21, and needs to continue to mature. Part of that is knowing what your strengths are. Muamba no longer attempts 40 yard cross-field balls because he has realized that he doesn't have that ability.
2. Tactics. Since Owen Coyle has come in he seems to have instructed Muamba to play shorter passes and not look for the long ball. His philosophy is to keep possession, rather than lumping it up the pitch as quickly as possible.
3. Positioning. It seems that Coyle has instructed other players, especially in the midfield, to get closer to Muamba when he wins the ball, so he can play shorter and more accurate passes. Tamir Cohen has struggled with this a bit, but Ricardo Gardner did it brilliantly today.
It really comes down to Coyle putting players, particularly Muamba, in a position where they can succeed, which is all a good manager does.