Use all the graphics your pc can handle.It's much better to see clearly all the details and to be able to see the clouds and all the shadows.Especially the shadows are very important.A defender ,camping in a room,can see a shadow from an enemy , projected in the wall as he enters.It's a huge help.Also adjust the brightness so you can see clearly in the darkest corners of a room ,where an enemy camper might waits for you.
In case you made a mistake or a false move, don't worry.You can still benefit from it.Imagine you accidentally pull the trigger ( not me ;) ) and you don't have a silencer (very wrong).The enemy will be able to see you in the radar , and will close on you shortly.Take advantage from it.Get to a nice defensive position that will give you better view or better cover.Put a trap waiting for him or them.(claymore next to a barrel or a car) ,or even better,run quickly (and carefully) to the other side of the map and make a quick plant(if you are attacking) . Until the enemy gets there he will have lost precious time.When an enemy has only a few seconds to defuse it's possible not to try it.There is not enough time to search for defenders and to defuse.A light usage of brain power and some easy tricks will get you far.
It's important to study the enemy and learn from him.What are his habits,what weapons,perks and killstreak he uses,what are his favorite routes and how much time he wants to move.Learning that,you can predict many of his moves.That gives you an advantage.You can earn this knowledge from a face to face meeting,from one of your killcams or from watching your teammates playing while you're dead.Especially the killcams can reveal to you many of the enemies camping spots,and routes.You can see where an enemy camps,if he have claymores,another teammate with him,where he looks and many other things.that way you will be prepared in the next round and you will choose another approach.Watch out though.While you study the enemy,he studies you also.So if you managed to kill him in a previous round don't try the same way cause you might die.You must have many different routes and tactics as long as hiding-camping spots (if you are defending).Depending on the enemy you must adjust your gameplay and tactics.
A force multiplier is an object ,a weapon or a perk that if used right and wisely can multiply the benefits that you can get from it.Such a thing is the perk recon.Recon can help you in many ways.You can benefit from it in many ways cause it affects not only your grenades but also your weapons if you got it pro.It marks your enemy in the radar and make them visible for a few seconds.Imagine a stunned or flashed enemy that cannot see or move,visible in the radar next to you.He is already dead.Especially in small maps or narrow areas you can prenade the enemies and mark them for all your teammates.All of your team can benefit from it.That's a force multiplier.Even if you are alone against many enemies you can get a lot of help.Another thing is the right usage of your knowledge.Many weapons can help you in many ways.Use them wisely.Use the knowledge in the right way.Imagine that you start a round with a predator you earned in the previous round.Using the predator is going to give you one or more kills if you are lucky enough,but that's not the only thing you can earn from it.You can also see in the monitor where your enemies are.That's a knowledge you have to use.Imagine in the same example that one enemy has called an assault drone.Using your predator you can easily take out the drone.But that's not the only option you have.You can kill some other enemy that maybe rushes and threatens your teammates.Then you can go in the spot you saw in your predator monitor that he was camping in order to use the drone.He will be busy using his killstreak so he will be an easy kill.Use your knowledge wisely!
It's very important to use a weapon that suits you.A difficult weapon that you can't handle will put you in an unpleasant position.It's also crucial to choose the right weapon with the right class.A rusher for example, must choose a smg cause of better mobility and not a lmg.Remember,the final weapon is the brain!
When you guard a place (especially open spaces) like a building,a bomb site ,a far passage, you must check all of your FOV (field of view).If your eyes concetrate in one small near object , you won't be able to see the rest of the visible area.You must look somewhere far and remain still , so your eyes can feel any small changes in the background.If you move constantly ,your eyes won't be able to see the very few pixels in the screen that changed.
In order to achieve the maximum surprise to the enemy it's very important to get to a specific key-point before him.This key-point might be a neuralgic place in the center of the map,or a specific place behind enemy spawn.If you get there,then you can take a defensive position and wait for the unsuspected enemy,or (most important) in the case of the spawn,you can easily take out many enemies cause they won't expect you to be there so soon.In many cases,many players are spawning late cause of lag,or cause they choose a class for too long.In small maps you can easily surprise the enemy and take him out.The advantage is already yours.Many good rushers depending on the map,know many different routes (for both spawns),and how many seconds are needed to get to a specific key-point.Practice and surprise!