there are many different ways to harvest.. the way you do it is all up to you.. but, you can either cut off an entire branch, and hang the branch in a nice dark, cool area.. or, i have heard that some people cut the entire plant down and hang it that way..
or, you can cut the branches that have buds that are finished only down, and leave the ones that look like they could use some more time up.. this is called double harvesting, and is a great way to increase yields by letting some of the buds that weren't getting as much light get more light by removing whatever may have been blocking the light from them..
and if you leave about 1/3 or so of the green on a plant and put it back under 24 hours of light for about a month or so, you'll start to get new vegetive growth from it.. or you can simply take clones off of it, clones are simply a cutting of a branch that you then root, and grow out the clones after the mother plant is done with flowering..