When performing back barbell step-ups, find the proper step height first before playing with the load. Start with an empty bar and a low step position, and gradually raise the height until you find a position that is appropriate for you.

Once you find the right height, you can gradually increase the load staying within the prescribed rep range. Remember, the reps dictate the load (not vice versa) and always emphasize quality over quantity.

To learn more about this staple exercise, check out Step-Ups Develop Muscular Legs.