step 1. choose a gun. choose a gun you like. if you're not comfortable with that gun then you might not do well. try to choose a gun that fits your play style too.
step 2. perks. if your are sneaky use perks that hide you from other players like assasin. if you dont mind being seen use sleight of hand or scavenger.
step 3. equipment. try to use something that goes well with your play style and your gun. ex. if you're using thermal optics, try smoke grenades. if you are using a submachine gun you can move faster on the map, so c4 might be helpful to kill groups or objectives.
step 4. kill streaks. for support use advanced uav or uav to find their positions and to help you're team. on assault use predator missle or care package. you can defend a care package and kill people trying to take it. for specialist look at you perks and pick what you think will be helpful to you.
step 4. deathstreaks. use what you think will help you. i use matrydom or revenge. matrydom seems silly, but those frags you drop can get double kills. revenge is helpful in team based types since they always are near more enemies, ensuring you there is stuff to kill.
step 5. PLAY! a good begginer game type is team deathmatch. its simple just kill the other team. domination and kill confirmed are a bit trickier but not hard. my favorite game type is search and destroy. you only have 1 life and play as either bomb planters or defenders and have to defend or attack two bomb sites.
these tips were brought to you by me and my expierences with the game over time.