Something I've found helpful is pre-heating the board (e.g., with an under-board IR heater) before breaking out the hot air. As another poster has mentioned, chip-quick is also great stuff.

If you're trying to de-solder a BGA component, I can't help, but any other surface mount stuff check out Chip Quik Alloy. It's a super-low melting point solder that you can use to take off pretty much any non-BGA component with a standard iron and a pair of tweezers. Cleans off with braid.

Use higher airflow (including a larger nozzle) and lower temperature. The temperature calibration might be a bit off if the soldermask gets damaged by air at 300°C. Preheating, which has already been mentioned, also helps.