Bent Over Row Tips:
Make sure you bring the bar up to the correct position. Do not bring it up too high (to your chest) or too low (to your stomach).
Control the weight throughout the exercise. Don't allow it to drop quickly and pause for a count of 1 at the top of the movement.
And finally (most importantly) keep your back straight! If you bend at the back, you're using to much weight. Keep your head up, and eyes looking forward throughout the whole movement. You might want to use a weight belt and squeeze the back of the belt with your lower back. This will ensure that you keep your back straight. Do the bent over row in front of a mirror or get a training partner/personal trainer to check your technique.