I don't know about for MMA specifically but I usually plan my running workouts for long term, and I usually get good results from planning a 12 to 16 week schedule.

The specifics specifics of the run depends on your goals.

 

Sprints, interval running, BW circuits, sandbag work, etc.

 

I think that HIIT (High intensity interval training) is the best, I had that recommended to me on this forum and it seems to work really well. Break up the run, you'll get a better work out if you don't fall into a rhythm, use a jog/sprint combination, you could include a walking period if you like, hills or stair climbs are good too. As I said you'll get more of a work out like this rather than say...jogging the whole time. It makes sense too because this is the sort of work out you tend to get during a fight. You need to ability to explode when you are tired and keep up when the other guy pushes the pace etc etc.
As for how often you run and how long your run should last is up to you depending on what you are training for. Anyway, hopefully this will give you a rough outline or at least some idea's that can be thrown around.