I suppose it depends on what level of play you are playing (or hope to play,) your age and how active you are. If you are active or regularly participate in pick up games with friends/family, attend regular practices and games, etc, you may not need to do much extra. I'd suggest spending as much time as possible actually playing with others, as there is really isn't a better training program. If this isn't possible for you and you are trying to stay in the best shape possible, you might benefit from some training. I wouldn't focus on miles, but more on time and type of exercise. Maybe something like this:
-20-30 minutes of regular running 1-2 times a week
-Time with a ball: juggling, turns, moves, cuts, shots against a wall, etc. 2-3 times a week.
-Sprints: Break this up and make it fun: Straight sprints(without/with a ball,) zig zag through a course, squares (running around a small square facing the same direction,) stairs, make up your own. 1-2 times a week

20