the Kill/Death ratio (KDR): is how many total kills and deaths u get in-game.
if u have more Kills than deaths(low) in-game then KDR will increase, if not then it will Drop.
There are some tricks that can help your KDR increase abnormally ( no hack ) , call it cheating in your KDR but I advise you not to do it . KDR is nothing and it just makes your profile more sparkling , skills and tactics you need to have it. And more importantly, teamwork in battle Xd