When training if its training on the court or in the weight room you need to train correctly. If you are using improper form you will get very little if any benefits from the work you put in. 

PERFECT PRACTICE MAKES PERFECT

Common mistakes in the weight room:

1) Squats: when doing squats, keep your back straight and your knees should not pass your toes. This will reduce back pain. 

2) Full Extension: Practice full extension especially with Calf Raises and Leg Curls

3) Lat Pull Downs: With a Lat Pull Down you should NEVER bring the bar behind your head! This is not good for your body. 

4) Squat Jumps: same as Squats but when landing make sure you land like a cat and make very minimal noise while landing. This will reduce knee pain and injuries.