Warming the can also makes too fine a mist if it's too hot and can waste paint. Frequently removing the can from the water is a good idea, and stop heating when you shake the can and the bearing is moving around freely inside. It doesn't take very long at all for the can to pressurize.
Best bet is to keep the can inside for an hour or so before using it to let it get to room temp, then shake vigorously before spraying.
