Read this http://www.josephson.com/clean.txt
I use a $80 make up brush. It's super super soft and made from natural fibres. I stole it from my wife, she was super pissed. bahaha
Just go really really slow and super soft. Use a dry brush first to get any big particles off then diluted ISO with distilled water. Again super soft and slow slow slow. Make sure the diaphragm is completely dry before plugin the mic back in. You may find after the damp brushing slight water droplet marks on the diaphragm. Use another dry brush after the damp brush to get rid of these. Make sure the brush/s are brand new........
Happy cleaning!