For the begining I'd suggest a trapezoidal shape for your chassis, maybe a half fairing would look nice (sort of flipped boat), example:
Then, the track would be better if the wheels were denser, so it doesn't just look like a few wheels. Also make the side-most wheels a bit higher.
Then make a turret, attach a gun to it, and add some missiles.
Here's a small missile with a hard warhead:
Last time I made a tank was long long ago, maybe even 1.4
This one was focused rather on functionality than looks. It ha grenades, missiles and a main gun.