Another important tip and something to keep in mind is what you have equipped. This is mostly towards Perks. If you like being stealthy then you should use Ninja, Marathon, Lightweight. But if you want to be one of those people who get the fast kill streaks use Hardline ofc.
When choosing perks don't mix and match, use perks that would go together. Also when choosing your kill streaks be smart about it. If you are using Hardline I suggest equipping the low kill streaks because you can get them the fastest (IE: Spy Plane, Counter Spy Plane, Turret/Napalm/etc). Also when choosing a gun attachment do not use a Red Dot Sight on a gun like the AK74U because it is small and the scope makes it so much bigger.