Try to hold just your half the map, don't chase down retreating units or tanks, try to make them feel like they had a shot and not slaughter them and remove all hope so they don't come back...
Ehh, I usually don't do that stuff, anyways. Chasing retreating units, vet hunting, etc are all dick moves that piss me off (though I can understand why people do them), so I try not to do it to my opponent's much, not matter who they are.
But 'going easy' on someone for a the first few minutes of the game while you try to identify if they're a noob or not can cost you a lot, maybe even the entire game.
