Warm up & cool down. The next day (esp after leg day) I find the best thing I can do is some cardio. It might have to be "very low impact" (e.g. walking), but it keeps me from getting locked up. And also during the day (esp after leg day), esp if you have a desk job, make sure you get up every now & then & walk around - also helps you keep from getting locked up while sitting too long. Glutamine & I like my MSM for sore joints. And finally, throw in an ibuprofin or other OTC anti-inflammatory if needed.
Even though it hurts like a biotch the next day, and like an f'n beee-otch the day after that, get enough sleep (recovery!) and just remember, its a GOOD pain! That's your body telling you its getting stronger & stronger!