More brakes, less skidding and take time off when you're really sore. While I'm sure you're really excited, if you're having knee problems you need to allow them to properly heal so you can keep riding for years to come. As time goes on, my knee problems have gotten better from riding, but there have been times I've had to take a week off because I was having really bad pain that was keeping me up at night. Ice your knees for no less than 20 minutes after a hard ride, and take ibuprofen as well to help keep the swelling down (which is probably causing the pain).