Angling Your Armor Beats Upgrading The Gun
New players tend to chase the biggest cannon available. Veterans of tank games know survival usually comes down to how the armor is angled, not how hard it hits, and that difference shows up the moment shells start bouncing instead of penetrating.
A flat side is an invitation. Presenting armor straight-on to an enemy gives them the easiest possible shot - even thick plating doesn't help if it's facing the wrong way.
A slight angle can deflect a shell entirely. The same armor thickness turned even a little off-axis can bounce a shot that would have punched straight through otherwise.
Positioning buys more survival than upgrades do. A well-angled, modestly-armed tank often outlasts a heavily-armed one that keeps exposing its flat side.
None of this needs a tactics manual to apply - just a habit of turning slightly before trading shots, rather than driving straight at a target.