What are the best methods for cleaning really dirty lens elements?

I bought old M42 Pentacon 50mm f1.8 lens from a car boot sale. It works but is pretty dirty and it has also dirt inside (no mould/fungus though).

Opening the lens is not a problem but I would like to know how to get rid of grease and other dirt on lens element. I don't have access to ultrasonic washing machine. Undiluted isopropyl alcohol (IPA)?