I found body rows helped me work towards full pullups when I started. I always threw in a few sets of body rows after my simplefit workouts and really concentrated on the feel of my elbows and lats pulling back and down and really squeezed the bar or towel tight (a strong grip will make pullups easier as well). You might also try greasing the groove, where you do a single pullup (or in your case a single set of subs) but do them through out the day. Just keep in mind that sometimes less is more. If you're working hard enough you'll need a rest day to let your muscles recuperate so you can come back stronger.