Preacher curls have always been the favorite of all time greats like Larry Scott, the king of full, long biceps. I never like to start with these though. This is an exercise that's simply "meant" to be done with a pumped arm. Any variation, like the single-arm machine curl shown here, should be done after hammer curls or other bicep exercises.

Related:  More Arm Training Tips From John Meadows

Related:  The 10 Best Biceps Training Tips