You can quit by using the @QUIT command, or by just closing your client. The effect is the same.
Alternatively, keep in mind that you can remain idle in the game for as long as you want. If you think you'll want to play again a little later, use the DOZE command to take yourself off the WHO list and remain connected.
You do not need to save before quitting. The server automatically saves all game information, including character status, at regular intervals.
You should, however, take care to quit in a private location, such as inside your ship or in an apartment. Your character will still be in the game world, asleep, and other players can still move you around while you sleep!
Also take care to land your ship and power it down before quitting. If you leave your ship in space while you sleep, it is vulnerable to theft or destruction.
Disconnected players are invulnerable to most attacks, such as unarmed combat. However, this protection does not kick in for several minutes, so disconnecting is not a viable option for avoiding attack.