Don't Be Afraid to Use the Mirror

Mirrors are the best way to monitor your form and help avoid injury. The following are some things to keep in mind to avoid doing an exercise wrong:

• Your barbell should be parallel to the floor throughout the exercise. If it is cock-eyed, then you are exerting more force on one side. You may need to use a machine to help with form or possibly need to shore up one side (do some unilateral training)
• Watch your back position when doing squats, dead lifts, rows or any exercise where you bend over. Your lower back should hold its natural arch; if it is rounded you need to use lower weights until you perfect your form
• If your upper body moves back and forth while doing curls, rows, or presses you are not performing the movement correctly and need to re-evaluate the amount your lifting.
  

For any of the above issues, talk with a professional to correct you form and determine the amount of weight you should be using.