In general, I'd recommend changing your routine every 4-6 weeks since your body quickly gets used to doing the same thing all the time. Doing a full body routine that includes a few exercises for each major muscle group should be sufficient as long as you're using a weight that is challenging and fatigues your muscles at the end of the set.
Hope that helps,
"You may have a fresh start any moment you choose, for this thing that we call "failure" is not the falling down but the staying down." Mary Pickford
"No matter how slow you go, you are still lapping everyone on the couch."