I love observing people in the gym mainly so I can snag some ideas from what everyone is doing, good and bad. One common form problem I have noticed is that many people do not practice good form in their wrists when doing lifts with barbells or dumbbells. The problem is that poor wrist form can lead to sprains and strains to your upper body, not just your wrists.
So next time you're lifting at the gym, make sure your wrists are inline with your forearms and that they aren't bending too far forward or backward. Chances are if you can't maintain a relatively straight wrist-forearm line, then weight is probably too heavy. Go lighter and focus on form before upping the weight.