A few pointers and a little advice.
The heavy tank isn't for everyone. Most owners of TT prefer the light tank; even I prefer the light tank in scrum. But I don't play scrum very often...
The heavy tank is like driving a huge watermelon with a bullseye on the side.... it's slow and big. This means that it's easy to hit, especially for the inexperienced and/or demo players. As such, you have to use the terrain carefully and avoid going out into the open, especially when you're low on health. Keep in dense cover, even some of the rocks are large enough to hide this big boy. If you get into a mix of 2-3 tanks, a wounded heavy tank will be the first to get destroyed (big, easy target).
The advantage of the big tank is its thick armor, increased shot power, fast turning abillity, and stabilized weapons platform (auto-leveling turret). However, you only get 3 shots/clip, so you must be patient and make the 3-shot burst count. In the other tanks, it is easy to pepper an area with shells... the heavy tank's cannon is more of a precision weapon. Target practice is a must; this requires a steady hand... if you're a heavy espresso drinker, go play the light tank. The heavy tank is the "nerves of steel tank".
The physics of the heavy tank are not as they should be. Currently, the light tank can plow the heavy around the field as if the heavy were made of styrofoam. Conversely, the heavy can't budge a stationary light. The good thing is that the game is being tweaked; the developers are excellent at listening to players' comments (find Joe on the Forum).
In close-quarters, one-on-one scenarios with medium or light tanks, the heavy is usually at an advantage. Often, howevever, your opponent will attempt to retreat. Then it becomes target practice as they fade into the distance....
Check out these threads from the Forum:
Heavy Tank Woes
Heavy tank about right
more later
