Ask a Pro. If you have any doubt about how to use a machine, ask a Personal Trainer or fitness center staff member. Don't overtrain. Your body needs time to rest, so make sure to take days off from strength training. Good spotter. If you have a spotter, make sure they know what they're doing and you communicate when you need help. Keep your back straight. When doing biceps curls with free weights, keep your back straight and your knees slightly bent. Pay attention. A lot of injuries are caused by simply getting distracted while your strength training. Pay attention to what you're doing. Proper technique. Proper technique is the key to avoiding injury while strength training. If you're not sure about how to do something, ask. Start light. Start out with light weight that you know you can lift. You can always add more. Stretch after warmup. Make sure to stretch out the muscles you're going to be working after warming up a bit. Too much weight. The most common cause of injury is strength training is trying to lift too much weight. Work your way up.