Cut each branch at the stock. At harvest time, after all the dead fan leaves have been removed, leave the plant in the earth if possible (if it's a hydroponic plant, obviously, you won't be able to do so) and use a pruning tool to cut each branch off where it meets the main stalk. Start with those nearest the ground and work upwards.
If your plant is especially large, it may be necessary to use a pruning saw for the very big bottom branches, which are often the thickest.