Partial Reps
Perform reps over a partial range of motion - at the top, middle or bottom - of a movement.
Forced Reps
Have a training partner assist you with reps at the end of a set so you can work past the point of momentary muscular failure. Your partner helps lift the weight with only the force necessary for you to keep moving and get past the sticking point.
Drop Sets
After completing your reps in a heavy set, quickly strip an equal amount of weight from each side of the bar, select lighter dumbbells or move the pin up on the stack. Continue repping until you fail, then strip off more weight to complete even more reps.
Rest-Pause
Take brief rest periods during a set to squeeze out more reps. Use a weight you can lift for 5-6 reps (5RM) but do only 2-3 reps, rest as long as 20 seconds, then try for another 2-3 reps. Rest again briefly, then try for as many reps as you can handle, and repeat once more.