Farm the activities that give you a chance of an exotic. 3 nightfalls, 3 deathsingers, 6 crota easy then hard, 6 atheons, 3 gorgon chest. Gatekeeper on vog drops exotics too i believe. 21 areas for sure. My success with this is ok. 1ghorn, 5 nlb, 2 truths, 3 red deaths. In the last 3 weeks or so.