When I first starting going to the gym I would watch other gym goers and repeat what they were doing, assuming it was correct and that I didn't need to spend any time with a trainer. Before I smartened up to the fact that the folks I was mimicking were just as clueless as me, I incurred really poor habits and a bit of back pain.
So, try not try to lift like the guy next to you in the weight room — unless they're a trainer, they could be doing it wrong. He may seem like he is getting in a killer workout as he grunts, swings the weights, and holds his breath while lifting 30 pounders, but that's his thing, not yours. Plus, it's not a race. Strength training is a personal thing that should be tailored to your individual strength and done slowly while using proper form and weights. So the next time you see an exercise that you'd like to try ask a personal trainer to show you how to properly do it, or look it up when you get home.