Srayed with a water sprayer. The plastic types you can get from all garden centres and cheap shops. Every few days or once a week give it a spray with tepid water.
A lot of plants can benefit from this as central heating drys the air inside your house.

Just make sure the sprayer you get can be set to a fine mist rather than a hard squirt - you want the mist to be very fine.

thanks

just make sure your bonzi is a tropical type or it belongs outside

Misting bonsai is not a very effective way of keeping the humidity levels around the plant high. A more effective way is to fill a tray with pebbles or grit, fill water to the top of the pebbles/grit and stand the bonsai pot on the tray. The evaporating water will keep the air surrounding the tree humid.

Spraying or misting the tree keeps the leaves clean and free from dust.
Use tepid water so as not to shock the leaves causing leaf drop.