hi there 

I know you are here to get some quick pro tips bout cod

First if you are a battlefield player you are recommended to get the hell out of here 

so for starters

The aiming

If you are starting your career as a fps gamer then you should know two things

1)Crosshair

Ok now what is a cross hair ? It is nothing but the aiming reticule you get on the screen.

The main reason developers added cross hair to allow players to scare off their foes game NPCs are just simple bots.These thing are programmed to dodge and avoid fire from you so if you just spray an area with bullets to make them run for cover you are doing good!This will help you in cooling the combat scenario a lot and this will also allow you to get some cover.But if you are using this to kill then you are wrong!Use crosshair only too kill NPCs at short range or to scare em off.

2)The Iron Sights and scopes

1)Ironsight 

It is the basic attachment given to you by default.Use ironsights to take down enemies from a safe distance with killer presicion. If you are starting from modern warfare series then you will hear sheppard howling to aim down the sights.

2)RDS,Holographic,Mars,ACOG,Thermal sights

RDS are one of the cheapest and most effective sights available in multiplayer loadouts.RDS are just blessed when engaging in medium ranged combat.They don`t provide magnifiaction but will definetly let you mow down hordes.Holographic sight now these things are nothing but a RDS with a big reticule these are also usefull though.Now comes MARS sight well you can find this sight in a few guns but these are very shitty anyway I would preffer you to use the holographic instead.

Now comes the ACOG sight provides slight magnification and allows you to get headshots easily in long range combat.

ACOG sight

Grenades and explosives

Well having tough time flushing enemies out of flank eh?Tossing a grenade will always flush cowards hiding behind cover easily.

Flashbangs will always do the trick to make enemies blind and making them vulnerable to fire!

Smoke is good for escaping

Under barrel grenade launchers are really good for taking out groups of enemies.

Well I don`t have much time so follow these and they are bound to help

will update later