Physical therapist gave me a ton of leg stretches and stuff to do. I also do back and shoulder/arm stretches and a 10 minute medium to fast pace walk on a treadmill beforehand to warm my leg muscles up. Never stretch "cold" as you muscles need to warm/loosen up a bit before you go head first into stretching. I notice a significant difference in flexibility and pain when I warm up first. My routine takes around 40 minutes and I try to do it 5 days a week but not always. I definitely wouldn't lift on a day without stretching first. I used to not because I had been told it can actually lead to injury as it can weaken muscles but then I hurt myself and say a physical therapist and they told me that's dumb and I should always stretch. So not I do and I haven't messed myself up again as of yet.