Obviously you want to get all of the dirt and sand out of any moving parts. You can do it by wrapping the engine and electronics in plastic and patiently spraying it with water from a squirt bottle or hose and wiping the dirt away. OR if it's seriously dirty, just take the engine and electronics off and throw it in the top rack of the dishwasher. Just make sure your mom/GF/wife doesn't know...

Either way, once it's washed off, you can dry it with compressed air or leave it sit to dry. Then, make sure you lubricate all of the bearings and moving parts.