I'm just terrible at this game. Trying to do the Jolly Holiday quest now that I got a Last Word and in a 3 game period I went from 0% to 25% then back down to 0%. Now I can't even get a match where I get a positive gain.
If your team sucks or the other team has its sync going just un-equip it so you don't lose %. When the heavy ammo is coming re-equip, grab the heavy and wait 1-2 minutes and then chain kills to raise your %. Getting kill streaks will give you bonus %