Here is a good reminder to keep an eye on your ground cover like MOSS for example and make sure your bonsai does not suffer from a tightly packed surface. If not checked, moss can make it difficult for water to properly penetrate the surface and thus giving your bonsai adequate watering.

Make it a practice to check that the water is flowing out the bottom of the tray, also try using the technique of poking a pencil into the soil to allow for good airation (be very careful not to damage roots by doing it gently and if you feel resistance, move over a bit).

I cover this in detail in Mastering the Art of Bonsai HERE