You need to use solvent. Hasselblad / Zeiss used to standardize on Windex. Kodak lens cleaner is also good, and ROR (http://www.ror.net/
) is also good.
Breathing on the filter unfortunately deposits a coating of water, and, if you are unlucky, saliva, which will just smear onto the filter.
Or go here, if you want to go "all the way": http://lenses.zeiss.com/photo/en_DE/..._products.html
The method is to:
1. blow off the surface that you want to clean to get rid of dust
2. moisten a cleaning tissue with fluid and wipe it all over the surface, gently
3. with a clean tissue, dry off the surface, gently
4. do NOT touch the surface of the tissue that will come in contact with the glass, with your fingers. If you do, you'll just transfer your fingertip skin oil onto the glass and ruin the efforts. This means that you must only touch the tissue at the edges, including if you have to roll or fold it up into a more manageable wad