Become Familiar With the Map
Learn the map as quickly as possible to find hidden spots for a sneak attack on your opponents. Take note of the areas that are exposed to these sniping locations so you can avoid them when you are walking around. If you are killed by an opponent, watch the Kill Cam to find out where he was hiding.
Creating a Class
When you first create a character on Call of Duty, you are limited to the standard classes that come with the game. After you gain enough experience points to advance to level four, you will be able to create your own class. You can then use any combination of perks, grenades, and weapons that you wish.
Choosing a Weapon
Unless you are very skilled at aiming, you should stick with a balanced weapon like the MP5. This submachine gun has decent accuracy at medium range or closer and inflicts a moderate amount of damage to your enemies. A light machine gun like the SAW is also a good overall weapon. It gives you a higher rate of fire than the submachine gun, while still being accurate and powerful.
Firing Weapons
Use the single-shot or burst fire mode whenever possible to conserve ammunition. Automatic fire mode also reduces your accuracy because of the gun's kick. Every shot becomes less accurate than the last, making it almost impossible to keep your weapon on target throughout the entire clip. Burst fire also makes it easier to hit an enemy that is ducking behind cover or running across the combat zone because you can stop and adjust your sights before firing more rounds.
Using Perks
Learn which combinations of perks are effective and which ones may expose you to enemy fire as you set them up. Sometimes it is not worth the time it takes to select the items from your inventory. A good example of this is using the UAV jammer while you are shooting a weapon that makes a lot of noise like the LMG. When in doubt, keep your strategy simple and use the most efficient method of killing your opponent.