One of the things I look for when watching clients form in any compound leg exercise is the knee tracking correctly over the toes.

When performing external rotation exercises for the shoulder I often see it performed incorrectly. There are a couple mistakes I tend to see

One of the things I have found to help clients learn to do a new exercise in the proper form is doing the exercise first with no wieght

Working on and trying to correct muscle imbalances, structural imbalances, flexibilty and mobility issues and other problems are important

The squat is one of the best exercises one can do but it can be difficult to learn and to master.

When doing isolation work for the triceps like this exercise seen here (lying tricep extenstions) be sure to not move your elbows around.

One thing to keep in mind anytime doing chin ups/pull ups is to keep your hips from swinging forward to help propel you upwards.

A thing I like to use to teach clients proper form on barbel split squats and step ups is using a plastic pipe instead of a barbell to start

In a video here of my client Justin we are doing split squats. I always stress the importance of proper form on all exercises,.

There should never be an excuse to not perform the negative (eccentric) phase of a exercise in strict form.