Since a lot of people apparently don’t know this:
Target Priorities in Combat:
Tanks must be destroyed as quickly as possible. Tanks can single-handedly decide the outcome of an entire battle if they’re positioned correctly. To do this, use anti-tank guns, saboteurs, markings for aircraft, and anti-tank soldiers. If you’re playing as a tank yourself, you should ALWAYS prioritize destroying an enemy tank over infantry.
Aircraft can also cause immense pressure and supply problems. Build AA, spawn an AA vehicle, or point this out in chat if you’re currently unable to do anything against an aircraft yourself. If you’re flying a plane yourself, destroying enemy aircraft ALWAYS takes priority over everything else.
AA, anti-tank positions, and machine gun nests should also be taken out quickly depending on the situation. Any soldier can handle this—use grenades, TNT, targeted fire, or suppressing fire, etc.
Always mark large groups of infantry, tanks, and positions, as well as suspected spawn points.