Originally Posted by Lurker27
You'll want a mix of mobility/flexibility, endurance, and speed work. Honestly, running sprints and training legs (squats, lunges) will be most beneficial.
That said, the best way to get better a paintball will be to drill paintball more
Pretty much exactly this. Paintball isn't the epitome of athleticism and doesn't require much specialized athletic skill. Just being in good overall shape is what you should be shooting for. Aim to get faster and be able to play ~10 straight points without a drop off in play. Working on flexibility is always key.
As long as you're in decent shape, you'll get a lot more out of drilling and playing more; but, of course, working on speed and endurance doesn't cost anything.