Don't neglect hip flexor work. Often gets ignored & can greatly improve your leg turnover rate and increase your 60 times (run stairs or steep hills - up and down, wear ankle weights while lounging around, walking, and sleeping - don't run with the ankle weights on). Also, don't squat without doing deadlifts (or some other exercise to strengthen your hamstrings) or you will find that you will create a quad / hamstring imbalance and have a higher risk of pulling hamstrings. Do not do leg extensions with weight - that machine put many doctors children through college