A good bulb blower to get the dust/grit etc off. Make sure it is lifted. Try a gentle wipe with a soft brush (the Lenspen brush - see below - is good). If stuck, then you face a wash job. If all that remains, after the dust/grit is removed, is significant fingerprints or oil marks from eyes/eyelashes, then consider a lenspen:-
http://www.lenspen.com/
Most camera shops sell them. Eg:-
http://www.digitalcamerawarehouse.co...egory948_1.htm
I have the MiniPro. It lifts human oil (organics) off easily.