You may think this is a no-brainer, but the bonsai has very specific watering requirements. Approximately once a week or so (when the topsoil feels completely dry) immerse the entire bonsai plant in a bucket or basin of water. Once the air bubbles have risen to the top, the bonsai has absorbed enough water.
Humidity is also an important consideration for the health of the bonsai. The majority of High Street available bonsais come with humidity trays and bag of pebbles. The humidity tray is unwrapped by the recipient, covered with the provided pebbles, and then the pebbles are covered with a little water. This will increase the humidity level for the tree, in addition to protecting the desk or table surface on which it is placed.