The ukulele is played sitting down or standing up, depending on what best suits the song. Sitting down is more comfortable for extended practice, of course. The most comfortable position is to loosely hold the ukulele by gently pressing it to the area between your hip and you chest with your right arm.
As with all instruments, your psture should be comfortable and relaxed. As soon as you feel your grip is secure and comfortable, you should try playing standing up. The left hand gently presses down on the strings for the chords while the right plays the strings using either the wrist for a more dynamic or the fingers for a more delicate response.
Ukuleles are particularly sensitive to humidity and temperature. The ambient temperature should be between 20° and 25° Celsius and the recommended humidity levels are between 45% and 55%. Otherwise, the wood could work or warp.
When storing the ukulele you do not need to relax the strings; keep it tuned. To clean the surface, you do not need to use chemicals. It makes most sense to wipe the surface with a damp microfibre cloth.