In my campaign I have found myself with three main fronts, one very hostle, one semi-hostile, one relatively peaceful. I keep one good command general on each front. The two who are defending (peaceful and semi-hostile) currently spend a lot of time developing the frontier... building watchtowers on hills and forts at choke-points. The other keeps pursuing my goal of eradicating the stinkin' Gauls.

The rest I use to manage my best cities and to deal with the random rebel armies that seem to pop up every once in a while. It's worked well so far. Also, it seems like it is MUCH easier to gain command stars than good management skills. Give a newbie general a good army and let him trounce a few enemies and he will go up rapidly.