That's the one where your spy is in the top of the map and you have to rescue her?
Well, I can't think of too many tips, but there are a couple of things I did:
You need a clear path to bring her down. Disable the nearby turrets. If they are ground turrets, attack with planes. If they are air turrets, attack them with ground troops.
If I recall correctly the enemy has one large, slow tank near the spy. I think you can just run by the tank as it's a pain to kill it.