How do you make your own sets and repetitions for a certain workout?

See how many you can do total without stopping divide that by 3 and try it in different sets.If you can do more then that add another set of whatever your # was.It goes on from there untell 6 if you getting to 6 sets of your # step it up by 10 more,and so on.Or you can just keep doing them untell you cant.Then stop then try it again,and again and again.Thats the best way,but sence most people wont do that because its too hard,Try the repetitions plan.