Yellow square farming food gives the lowest EXP and is only important at very early levels.

Red triangle farming food gives somewhat more farming experience.

Blue hexagons give more experience than red triangles and yellow squares combined.

Giant blue hexagons give a lot of experience but have a very large hit point pool.

Turn on the auto fire mode by pressing E on your keyboard, but keep in mind that it will slow your forward movement if you have barrels on the front side. Auto firing works great for the Octo tank that has barrels on each side.

At level fifteen player gets to chose his first tank class, his second at level thirty and some even get a third class at level 45.

The first four classes are:

Sniper - A long-range, slow-firing class that does high damage.
Twin - A rapid-fire class with solid accuracy.
Machine Gun - A rapid-fire class with the least accuracy.
Flank Guard - A higher mobility class that has two barrels.