Try to get a machine gunner when you use the Goliath. Without a machine gunner you're very open to Raptor attack. A good machine-gunner will be ready to jump out if a Manta appears, and use an AVRiL on it. As neither the machine gun nor the main gun are much use against the very agile Mantas. This is also a decent strategy against Raptors.
When attacking nodes, remember that sometimes its easier to target the bottom/base of the node with the main gun instead of the (sometimes nearly invisible) upper "bracket".
If only one bot is driving a tank, you can steal it from the bot by becoming the machine-gunner and then switching (using the 1 key (2 to switch back)) to take over the tank.