I see a lot of people, even experienced body builders in the gym using some questionable exercise technique. Hey we all do it from time to time and there can even be a time and a place to use partial range of motion and even some cheated reps. For the most part however, we should really try to practice exercise movements that use full range of motion, without swinging of the body or arms and with full pauses at the top and bottom of the rep.
Like anything in life, we can develop some bad habits so make sure to take a step back and just don't assume you are doing it right. I even suggest using a video camera and record your workouts periodically so you can see how you actually look while working out. It can be an real eye opener for sure but at least it will allow you to make corrections.
Watch my YouTube Video where I demonstrate some "how not's" and some "how to's" for using Proper Technique When Lifting Weights!