The M4A4 is the default weapon of choice for Counter-Terrorists in CS:GO, only to be surpassed by its Terrorist counterpart, the AK-47, due to it’s lack of one-shot-kill ability against opponents with helmets (only 90 damage). Still, you should aim to master both, since you will use them in most of your games. As a bonus the M4A4 lets you move the fastest among the rifles. On CT side it is recommended to buy the M4A4 as the standard weapon after the light rounds, when you are not playing AWP.The M4A4 is very effective on all distances, but especially for medium and long distance.
There are 3 ways to shoot using M4A4:
Tapping with the M4A4 is not as popular as with the AK-47, since you can’t kill an enemy with full head armor with a single shot. It’s still worth practicing for long distance combat. Just aim for the head and shot only once, wait until your (dynamic) cross is fully reset and repeat as fast as possible. This technique avoids spray effects altogether. Since it take only milliseconds, you can actually shoot pretty fast. Practice shooting at the exact same spot on a wall, until you got the timing perfectly.
Bursting with the M4A4 is the most effective shooting techniques. Against an armored opponent, 2 bullets to the head or 5 to the body will do the job. To practice bursting aim for the head and shot 2-4 times. While the first 2-3 shots are pretty accurate, after that you need to pull down slightly so compensate for the recoil. Practice this by shooting against a wall. If you do not have dynamic crosshair (most don’t these days), you know that the your aim is reset, when your weapon model is back into default position (it goes up and back while bursting). You can use bursting in combination with side stepping / strafing in order to be harder to hit. Use bursting especially for close to medium distances.
Spraying can be effective with the M4A4 in short distance fights against multiple opponents, due to its high rate of fire. Even if you don’t hit a headshot (for which you should always aim) the first hit will most likely throw off your opponents aim.
Spray patterns and recoil compensation:
Mastering the above techniques (especially the full spray) takes a lot of practice time to master. To speed up your learning curve, look at the following animated pray patterns by twowordbird. The first shows the exact spray pattern (without randomness) of the M4A4, while the second show the movement your mouse needs to do to compensate it. Try to follow the seconds pattern with your mouse, then try to repeat it in the game.