Problem number one - Posture. We all like to feel strong and fit. But sacrificing posture for weight is a giant no-no. I regularly see some pretty muscular guys all hunched over with their heads ducking forward while lifting. What a waste! The major problem is that they build muscle in an unhealthy way. It configures their physiology in a hunched over, disempowered way. Do they seem powerful? Yes. But I challenge you to seek health not just size. The two are not necessarily related.
Problem two - Not finishing range of motion. I saw more than one person this morning (ladies too) who performed an exercise at only a small fraction of their full range of the joint. While some movements and exercises are designed this way, many others (including those I saw) are to be done fully utilizing the movement of the joints. This contracts the body, wears on the joints, and even has some negative effects on the brain! We encourage you to complete the capable range of motion to fully stimulate and bring health to the joints, muscles, bones, and nervous system.
These two issues are seen at every gym across America. It always makes me cringe. When you get your workout in, make sure you're following these two principle; maintain good posture and go through the full range of motion. If you have questions ask a trainer. Most will be quite knowledgable. Exercise is critical for health. You'll get far more out of every trip to the gym if you include these concepts to your next session.