Note: This guide was written mainly in relation to Half-Life, made by Valve Software, but may be applied to other games.
Second Note: This has nothing to do with psychology, i just thought it was a sexual title.
In my opinion the best way to succeed in multiplayer is to always assume the other player is better than you are, and since you are probably a newbie the other player probably is. You shouldn't forget that, unlike in the single player game, when you are playing against other people they have brains that will always be picking out strategies. Therefore you have to make your strategies better so you're the one that takes the first shot that may decide who comes out of the battle.
Generally two strategies can be found, defensive or offensive. Overly Defensive players are big wimps, they will never enter a battle with anyone unless they are using a more powerful weapon and have full health and armour otherwise they will run away. Offensive players, on the other hand, will always try to win a battle no matter what, they will be the faster mover that jumps around more, they will also rarely stop moving. Unfortunately it is not a good idea to adopt a single strategy, the best psychological state to get yourself into is a flexible one, make sure you always know what your health is and make a judgement on if you should get into the attack, and anyway if you find the other player is better you could always try to confuse him and then run away. NARF!
Now I will go into more detailed psychological tactics that you will come across or may wish to employ yourself.
This is the type of player that finds an area on the map where there is something worth having and he sits on top of it killing anyone that comes close. They are frowned upon because they normally like to simply sit in one place all the way through a battle and just kill anyone that comes by. Don't worry if you get killed by a camper, just go pick up the biggest gun you can find and take your revenge, always make sure you visit that point often taking out the camper every time, throwing a barrage of insults at him at the same time. You'll soon get him playing like any good player should and this will make your time harder, which is a good thing because it makes you a better player. On the downhand he/she may just go sit in another point around the map, but never mind it just means your going to be more careful when moving around a map. I don't recommend that you should be a camper because although you will find it is satisfying to kill people this way, it is much more satisfying when you work to make a kill. They may be frowned upon in a normal deathmatch but when you start playing things such as Team Fortress they are an integral part of the gameplay to defend your base.
To lure a camper out of his hiding place kill someone near him and when he sees the ammo you may have left he will run to go get it or may try to ambush you. Ambush him.
Understand where a player will go
What you will find is that the newbie will not think about where they are going around the map and will just focus on just getting as far away as possible from any possible killer. The better player will be thinking as he’s moving, where are the next items that they can use. If they are running from you during a battle it is usually a sign they are low on ammo, you should just try and push as many 9mm handgun bullets into their head as possible before they have a chance to receive some health. Also the novice or a person who is just low on health will not look back, you then may find they make a mistake on the route they take and that you can ambush them, they will not know you are not following them but are in fact about to ambush them.
Reactions to Newbies
It's generally known that most people hate newbies, they usually get lost on a map, get in the way, lag a server and moan. You have to be the exception to the rule; you have to prove to the other players you are good. Firstly you need to know where you going around a map or people will soon get bored when they find you lost. You shouldn't ever get in way of anyone because you should be attacking them, don't forget to keep looking behind you. Never join a server that there you have a high ping connection,. Don't moan it just annoys people; go find another server with other newbies. Basically your aim is to make yourself seem to be a half decent player and aim to improve your gameplay.
First thing you must learn to do is to accept defeat when you are beaten and congratulate the other player at the end of each map. This will help you gain respect with the person you are playing which is a good thing because if you gain respect you are a better player. Why? Because you will get a better experience in the game as the other people treat you differently.
You must also realise that if you start to control a map and even the good players will be hit and their playing will be affected. Also if you find you are pimping maps on a server that the people you are playing with aren't good enough. It's usually best to play against people who are of slightly higher standard than yourself; this makes the game a much greater challenge and improves your game playing skills.
Conclusion: Try to avoid being a stupid-geek.