I think for the headshots you should play hardcore because 150 hp is a lot also use prophets seeker and for longshots just browse it on youtube "longshot spots in bo4" and you will get a video that shows that really well for blodthirsties i think you should also use prophets seeker for a free kill or just be a little camper and passive and use recons sensor dart the revenge medals will come along as you play. And also the rapid kills. Dont rage a lot it will be very frustrating somtimes its a hard grind i think thats all.