Wipe the head after every session. A dry cloth and a minute is usually enough; if the head has been used over oil, a damp cloth and a little soap will do it.
The heads come off with a twist — anticlockwise to release, clockwise to fit — so you can wash them under warm water and let them dry fully before they go back on. Do not run the body of the device under water.
Store it upright, away from heat, with the port clear of dust. Charge it every few weeks even if you are not using it, and it will be ready when the evening needs it.