Play VOG and hope for one of the weapon drops like Corrective Measure (a beast in the crucible) and buy The Calming fusion rifle - also heavy ammo always drops in the same spots, if you hear "heavy ammo inbound" then immediately run to one of those spots so you don't miss out - it's first come first serve. Lastly, only play Control, players are usually preoccupied with capturing zones and once you learn the maps you can learn the paths from zone to zone - for players who aren't too great at the crucible Control offers the best chance to have a decent k/d and a better chance for kills.