If it's only dust on the lens then can of air is good or a very very soft lint free static cloth. Most of them are coated though and they shouldnt be touched anyway.
As they are a lens - you should be able to clean them with the same methods that people would use, to clean a camera or camcorder lens. If you ask in a decent photographic shop, I'm sure they'd advise you on what to use. I use Pro-Clens - awesome stuff!
