Learn the maps - the easiest way is to stay on the outside edges and run around the outter edge of the map. NEVER RUN THROUGH THE CENTER! look at your heat maps and get familar with the "Hot Spots". Figure out what your play style is...are you are run and gun, campers, sniper, etc. and build your loadouts to fit your style.
To help your KDR when going around corners ADS (Aim Down Sights) this way you are less likely to be suprised. That half a second it takes to ADS can determine if u die or not. There is lots more you can learn over time. watch youtube video guides, they are helpful in most cases.
It's really just muscle memory and map knowledge, there's plenty of videos on youtube about that can help with tips and tricks but nothing beats just playing. Apart from straight up practice I'd say start with just bots, then try some Combat Training and when you get to multiplayer proper I suggest starting in Free-for-all or Team Deathmatch. The way they're set up in BOII you don't see many of the high scorestreaks you see in chaotic modes like Groundwar and Domination/Demolition which can be pretty hard going for newbies.
Have fun and remember that the only way to get better is to die....a lot.