Local car wash. Use the presoak. Scrub bugs off all the leading edges with a non-scratch scrubbing pad. For more serious grease/road grime build up, Simple Green and a plastic scrub brush (about once a year I pull the mufflers to clean the road grime off the backsides with Simple Green, and I get a little more aggro with the wheels and Simple Green). Rinse, but never use full pressure on electrical bits, air cleaners (if you're freaked), brake reservoirs or chain (if you have one). Roll it out and wipe it down with the car wash blue chami.
Never had a problem doing this for over 5 years.
