To ensure that you jump high while doing parkour, you need thorough training that will ensure that all your body parts and especially the legs and hands are strong enough. This training will include wall runs/climbing, landing and rolling moves.
Practice = Performance. Perform dynamic leg stretches daily. Start doing squats (with, or without weights) at least 3 times a week. You can do the non-weighted squats practically anywhere. When you're using weights with squats (be sure to have a spotter) go down slowly then, while still maintaining your balance, rise back up very quickly or "explode" upwards, I've been told that this will help give your muscles more quick, "explosive" power, kind of like they're spring loaded.