Elbow grease and lots of it, on the engine block use a soft brush toothbrush for the hard to reach area's, any engine cleaning product does the trick the spray on and hose off ones are s**t so do not waste your money on them.
The secret is to wash and polish your bike at least four times a day do what I do I have the wife wash and polish my bike every morning before I let her go to work.(if you believe that one I also have a bridge for sale)