Basically this is how you make your tank VERY powerful with a good combination of perks etc. When my friend and i did this we finished with me on 32 kills for 0 deaths and him on something like 25 for 0, Not only that but we got tons of points from taking conquest flags, got the ace squad ribbon, lots of anti explosive and anti vehicle ribbons etc.
Basically you want the tank driver to be a medic, you want the normal shell, and the guided shell, you also want to have the motion sensor, i also use zoom optics. Sometimes instead of the guided shell its worth having the canister shell for extra power against infantry, depends if your team is any good at taking out enemy tanks or not.
You want your friend in the gunner seat to be an engineer, with a rocket launcher and the repair tool. This way if you get into a fight and your tank starts to get damaged then he can hop out to repair.
Make sure your friend is always on the opposite side to where the fire is coming from so the tank can shield him, take out any enemies on his side (you can see them with motion sensor)
If your friend does go down whilst repairing, quickly hop out and revive him then get back on the move again.
Basically go from flag to flag capping them, dont mess around in the middle too much except taking out enemy vehicles. If you're capping flags the enemies should come to you.
You can apply a similar concept to rush by having the person in the gunner seat quickly plant the bomb then get back in and wait for any enemies to try to defuse.
Obviously, prioritize anyone who is firing rockets at you when you see enemies on your radar :P
One final thing i have to nag at all people playing BF3 is PLEASE for gods sake, mark tanks, mark helicopters, mark jets. when you're flying around in a jet, even with air radar, its very difficult to spot things until you've practically gone past them.
Edit: oh and when youre on the move, keep your eyes on the ground for anti tank mines, they arent too difficult to spot