Keep your lights as close as you can without causing damage to the plants. That will keep them short. Also look up LST (Low Stress Training). You can make your plant have more main colas with this method. I highly recommend it.
i always pin em while young everytime a new node grows up i pin it with bent coathangers^ then i top it and unpinn the whole plant end up with a bush with a stem like ure wrist
Induce flower a little early and cut out the bottom 2 or 3 nodes. Do this in conjunction with ample lighting for nice fat colas. Just add a few more plants to make up for the shorter veg.
LST(low stress training) them. That means to train them by bending them, and tying them down. You can make it do whatever you want pretty much. Just search LST to see some examples.
LST would be the best for space managment. Topping does help with the overall end result of the plants height, but then again I topped mine and one is now 63 inches and still growing...