Super Sets

Supersets are just doing two exercises back to back. So instead of taking a break after doing a set of chest presses (for instance), you use that time and do a set of leg presses and then keep going back and forth. It makes you work harder because you don't get the same rest and you can get more in in less time. I personally do most of my workout that way with the exception of squats and dead lifts. Those I do first and all on their own.