Step 1: The supported buddy position.
How it works: You will have two people. Out of the two, the one with the smaller gun will get in front and crouch. The person behind them will also crouch, resting the gun barrel on his buddy's shoulder for extra support. Ideally, the person should have the longer, heavier gun.
Sniper/spotter adaptation: The spotter usually has a smaller gun with a higher rate of fire. He will crouch down, with his gun at the ready. The sniper will then rest his gun on the spotter's back. Because of the difference in the guns, the sniper will take his time to get anybody at a set distance (depending on the quality of the guns, it would be, say, 125 or more feet away.) Using this example, the spotter would use his automatic/semi automatic weapon to take out anybody who got within 100 feet. The spotter is more likely to be hit because he's right up front. For optimal support for both people, the spotter will be supported by a low wall or other defence, and the sniper will rest on his back. This is good for a defensive position, when the sniper and spotter have been discovered.
Ambush or undiscovered position: You will have hopefully found a good place to hide. If not, you have to work fast. It doesn't matter who uses their buddy for support, but it should be the person with the longer gun. In this case, both people will communicate. You will both pick out one target, and shoot at the same time. If you're in a hidden or defended place, you both should be able to take out two targets or more before they've discovered your location, which is very effective for two people.
Capture the flag: When playing capture the flag, you can use this position. When you find the flag, you should automatically fall into this or some other defensive position. After you've looked around and found no enemies, the person in front (having the lighter gun) should run up and grab the flag. If necessary for a faster grab, the person running can leave their gun with their buddy, but this makes it harder for the buddy if they need to run.
Well, those are basic adaptations of the supported buddy position. However, this entire instructable should teach you how to improvise, and it includes things such as this.
It should look a little bit like the picture, but the spotter might have a gun.