I like 25 minute HIIT cycles (as others have mentioned, get your basic cardio together first). Thats 3 minutes warm up, cycles through 1 minute on, one minute off, 3 minutes cool down.
Otherwise, once a month front squat tabata, 5 minutes, 20 seconds on, 10 seconds off continually. Good fat burner, but its also really fatiguing, similar to a very high intensity match (5 minutes because my matches are 5 minutes, I guess that when I get my blue, ill up to 6).
Roll as much as you can, but also try to get some stand up game practice - the initial standing phase (and the up and down constantly you some times get) really seems to exhaust a lot of guys, so its good to get some practice in there as well (it seems to be slightly different cardio).
Circuit training, sprints, obstacles courses at speed are great also.
Good luck.