On Friday mornings I teach a Cross Training fitness class at Parrot Cay and after I typically spend some time at the gym talking to the guests and correcting form. I am still amazed at how many people are exercising in bad form and have back and neck pain.
The First Rule
If you are moving your legs or arms you must not move your spine!
Keep a steady neutral stable spine and you will get more work in your legs, butt, and arms with less back strain.
The Second Rule
If you cannot maintain form stop the exercise.
Pushing through a set with bad form is almost worse than not exercising at all! You will strain yourself and you are not getting the full benefit of the exercise, so what's the point?
The Third Rule
Use your abs, back, and butt at all times.
When you are exercising, whether yoga, pilates, or weight training, keep your "core" muscles constantly engaged to maintain optimal stability and form (see above rules).