C4 can have many uses, but not only for tanks. When throwing C4 you are limited to throwing 6 in total. Any more will cause the first ones to disappear.
When trying to C4 a tank, be cautious of what direction the turrets are facing. If possible, try to place the C4 on the sides of the tank to prevent being reversed over. Also, there are an increasing amount of soldiers who use a proximity scan on their tanks. This will reveal your position as you approach the tank. If you suspect the tank has a proximity scan, try to wait for a distraction. IE: if an enemy tank is shooting a friendly tank, take that opportunity to get close and plant your C4. With the upcoming patch you will no longer be able to detonate C4 when you respawn. In stead, know when to sacrifice yourself for the kill.
This is not the only way to terminate a tank, though. You can place C4 on a jeep or humvee and drive it towards the tank and quickly exit, the momentum will continue on the jeep till it hits the tank, and you are then able to detonate it. This method can be tricky, seeing if something hits your jeep it will explode with you in it. This applies to C4-ing friendly vehicles. Do not C4 a vehicle when a friendly is in it. If an enemy hit the C4 with any type of explosive, the vehicle will explode and the enemy will get the kill.
C4 can also work very well in Conquest or Rush mode. In Rush, if defending you can either place C4 on the M-COM if you plan to stay nearby it. You can detonate if you hear an enemy arming it. If however, you like to wander off into the action, place the C4 in strategic places. After enemies arm an M-COM they are likely to stay near by, by hiding in a corner close enough to watch the M-COM. If you place C4 in these areas, rather than the M-COM it’s self, once you hear it has been armed you can easily detonate your C4 and get a successful kill. This can work while attacking as well. Arm the M-COM and plant a couple C4 to protect it. If anyone approaches to disarm, detonate it. In Conquest mode this is the same concept. Place your C4 in strategic places, where enemies tend to hide. Once you see the mini map is blinking or that you have lost an objective, detonate it immediately for the kill.
There will be some soldiers that will place their C4 in a certain location, stay nearby it at all times, waiting for someone to pass by it before they detonate it. I don’t consider this a strategy, and a lot of people would consider this a noobish act. You are free to try this, though I am not suggesting it, just warning to look out for it if you happen to see enemy explosives spotted on the mini map.
Further More, with every 100 kills with C4 Explosives, you will get a Service Star worth 2000 points. At 500 kills you get another Service Star and an advanced Dog Tag, displaying your total C4 kills.