9. Balance your training.
Whatever you do for one side of the body, you must do for the other side. Follow that rule in your workouts and you should be able to avoid injury and muscle imbalances. If you're doing squats (mainly a quad exercise), also do Romanian deadlifts (which hit the hamstrings hard). Your chest exercises should be balanced with back-training lifts. You don't necessarily have to do your balance work in the same session, but it should be done in the same week. In general, follow a ratio of two-to-one between your pulling-and-pushing movements. So if you bench-press on Monday (and most of the world seems to), you can do chinups on Tuesday and bent-over lateral raises on Thursday, for example. Every other pressing exercise you do should follow this formula.
10. Do it right. Form is key.
You may think you know how to perform the big four, but you could probably get more out of them. Here are some quick pointers for each one.
Squat: Begin the squat by pushing your hips back as far as you can. Keep your lower back arched and you should feel a stretch in your hamstrings. When your hips are bent, begin bending your knees and squatting low. This is what you need to squat maximal weight.
Deadlift: Use the same stance you would to perform a jump — your legs should be narrowly placed. When you bend down to grab the bar, keep your hips down and your back straight, with your shoulders directly over your knees.
Bench Press: Start with your head off the bench. Keeping your feet steady, grab the bar and pull your body up off the bench and forward, so that when your butt comes down on the bench your lower back is very arched. Squeeze your shoulder blades together. Your range of motion should be significantly shorter for stronger pressing.
Shoulder press: Flare your lats when the bar is at shoulder level. It will allow you to use more weight.