Placing AT guns but forgetting to check what they can see. Hey Hans, the grass is too tall in front, we can only see three hexes away!
Moving every available tank instead of using overwatch tactics.
Buying all that nice arty but forgetting to buy forward-observers.
Placing 88s on a hilltop which can see all the way to the enemy objectives and then having them all blown away by enemy 40mm AA guns on turn one.
