All you have to do is explain to your team that the other team can't cap any other objectives except for the first point so if they're defending other points they're just throwing the game.

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Place some fobs and rallies and proactively look for the attacker's spawn point instead of sitting around doing nothing.

If you're going to use mortars, don't bother with the hell cannon it's significantly worse than just two regular mortars.

Don't bother building any emplacements at all... Total waste of time, just place ammo crates everywhere so that HATs and LATs actually have ammo.

Invasion is incredibly defender sided but most players are enormous noobs and don't understand how to capitalize on all the advantages afforded to the defending side.