First, be sure to disable autoshrink.
Second, your autogrowth settings should be set to a fixed amount not a percentage. Also, don't rely on it. Set your databases to a size large enough to handle data growth without autogrowth for 3 to 6 months. You should monitor the databases and manually grow them as needed at appropriate times. The autogrowth should be used to epand your databases/logs when there is an extraordinary event that occurs (massive data import for example).