do 4 or 5 sets to failure (as in do as many as you can in one set) with a rest period between them every day or so. start slower, maybe do them every two or three days for the first week or two until your body gets used to it, then increase frequency. if i like doing them while watching tv, i just get up during commercials and do a set. it's a lot more rest than i would usually give myself in the gym but they aren't a really important part of my workouts, i really just do them because it's something to do when i really want to lift weights or something and i just want to be able to do more for the hell of it.