Hey Talbot,
I've topped lots of plants, for different reasons. I've used LST too, but since you asked about topping.... Take your cut, just above the desired node. Make a clean cut, close to but not so close as to damage the secondary growth/branch. I don't like to leave a big nub standing there, so I pick a spot where two nodes are fairly close together. Essentially, leaving two tops. Understand?.
Topping should probably be considered, a last option, but in some circumstances(mine) it can be just as effective.
