Stretching, squats, deep lunges. These are the ones that help me the most. Don't have to do any weight, but you need enough reps to make sure your legs can handle your own weight. If you're a bigger dude like me, you might want to work on cardio and losing a little of the extra pounds. That helps me a lot. Cardio for tournaments, but losing the weight helps with the flexibility.

Also, you can drink a lot of water and take a glucosamine supplement everyday.