I'm currently playing on 3 teams (2 outdoor and 1 indoor). If your goal is to be in shape for indoor....doing interval sprints is your best bet. I would try and mix in some longer distance running but short distant, sprinting stamina rules indoor. Playing shape for indoor and outdoor are very different IMO.
ie: run 10 yards, come back, run 20 yards, come back, run 30 yards, come back, run 40 yards, come back, etc.
There is so little time to recover in indoor as you are constantly moving vs. outdoor. Helps to find a team that has a decent amount of reserve players so you are not out there for the full 40 min.