Do wrist warmup and stretching exercises before you practice. Shake your hands around to loosen them up. Make circular motions with your wrists in clockwise and counterclockwise directions.
Wear protective wrist bands whenever you practice. They will help you stabilize your wrists and protect them from injury.
Do wrist-strengthening exercises with dumbbells. Let your wrists hang off the edge of a flat surface with your palms facing upward. Hold a dumbbell in each hand in this position. Gripping the dumbbells tightly, curl them toward you as much as you can, using just your wrists, then bring them as far back as you can in the reverse direction. These are dumbbell wrist curls, and you should do them often.
Practice freezes and balance. Start with the minor baby freezes, keeping your balance as long as you can. After a while, your wrists will become stronger and stronger, and you will be able to advance to more sophisticated breakdancing techniques that involve more wrist strength. The more you practice, the more you will get used to wrist breakdancing.