How do I build my biceps?

Personal trainer Matt Hart replies: Most of the biceps-building options in your gym just make for interesting training, so don't lose sleep over this. The elbow joint is a simple hinge so any exercise that closes this joint will exercise the three main elbow flexors: biceps, brachialis and brachioradialis. That said, the orientation of your hand during the curling movement will determine how much assistance you get from the brachioradialis, which runs down the forearm. This muscle is at a mechanical advantage when you do a hammer curl-type movement, where the palms are facing into the body, and this enables you to lift a heavier weight than in the usual palms-forward position. To this end, it's worth mixing up the hand positions a bit by doing different exercises.
It also makes sense to combine free weights and machine/cable routines, too. Free weights require the biceps and other elbow flexors to contract with variable force because the load at any point in time differs and is determined by gravity. Machine and cable exercises provide more of a constant load to the muscle and therefore develop strength throughout the entire range of movement. Again, a combination is best. Finally, and most importantly, whenever you're working the biceps, keep the shoulder joint locked in position. The only two joints of your entire body that should be moving are your elbows.