I only water it when it is near completely dry. I heft the small amount of soil to get a general idea of the amount of water in it. I've had it dry as a desert and moist as a swamp but the leaves seem to droop regardless. Its bizzare... I cant figure it out.
To Viper:
You can avoid becoming rootbound by using a wider, shorter pot. The roots will spread as long as there is space for them to do so. This is only, however, if you keep the plant short and flower early. When I chopped my last micro-girl, she was getting close to being rootbound at the finish.