Cardio is def #1. I had the misfortune of fighting someone much heavier than I and gassed in about 3 minutes rolling with him.
I would to heavy lifting, squats, and situps with weights (i usually do 60lbs, or 100lbs). Don't do ANY exercising the day before the tournament (unless you can guarantee to yourself that you wont feel cramped the next day), but the day OF, run and do light lifting to get your muscles flexed and your breathing up.
Yeah sprints break up your breathing pattern, much like in a match... I don't really enjoy running but if I do run, I jog on the street for 5 lights then sprint for 1 or 2 lights and then slow down to a jog for the next 5. Rinse, Wash and Repeat.
I know this sounds dumb but know the rules and ways to score points. Have a strategy going in there if you want to win. My first tourney I almost got DQed because I went for a heel hook out of habit. I also lost out on points I could've had.
I started running sprints and it helped alot. Im a big guy(was 280) and im down to 250 in about a months and some change. My stamina went through the roof. I just sprint from my dorm to and from classes during the week. And, drink water take vitamins eat right... etc.
do intervals, lots of stuff that raises your heart rate then let it come back down and repeat. such as spinting walking sprinting. tabata workouts are good. burpees then resting the burpees and so on. try doing 15 jump squat burpees the roll for 5 minutes and repeat several times.