Most of the time i just wipe it off, w/ a california car duster....
If she needs a good cleaning, i use that "car wash" liquid soap, in water. I'll use a regular towel on the plastics and stuff, and a scrub brush on the chain, swing arm, axle.......
I always dry it off afterwards...the water here is "hard" and'll leave spots, not only that but it dosnt take rust long to set in, if not dried..
Spray a little WD-40 on the pipes, and wipe it off....
If i'm really board, i'll break out the ol metal polish and do the rims and stuff...
Make sure you cover your air box and filter when you wash it... if you run w/ out a lid...