Instructions
Understand the combat range of each map. Maps are usually focused on long, medium or short-range combat. You should tailor your loadouts to each map type, so you are always well-prepared for the type of combat you will find.
Learn your way around every map. You cannot improve your K/D ratio unless you know where enemies usually hide, where you can stop and pick off a few opponents, and the best place to drop killstreak rewards.
Play smart instead of aggressive. If the enemy team is defending a point, do not blindly run in repeatedly until you get lucky. Find an alternate, unguarded route and sneak in. Knowing when and how to attack in a situation like this is critical in preserving your K/D ratio.
Stay with your team. Lone wolf tactics may keep you ahead on the kill counter, but you will need the assistance of other players if you want to stay alive. If your teammates protect one another, everyone's K/D ratio will benefit.
Stick with team-based game types. In a free-for-all match, you are going to be killed almost as often as you kill other players. Team-based game types give you a better chance of staying alive longer.