The article at the above link speaks to SLR lenses but it really does apply to all lenses.
I cannot stress strongly enough how important it is to clean your lenses and not simply by wiping them off with a cloth, I mean going through a process which is explained in the attached link.
The article is excellent and in most instances fits totally the methods I use to keep my lenses in top notch shooting condition. That means not only the optical surfaces but the electric contacts, the lens to camera mount, the camera mount as well. The inside of a lens hood is very important because the surface can trap dirt that makes its way to a lens surface.
I have written articles on this in the past in regards to sensors and lenses but this article is simply right on about cleaning optics.
This is a very serious process that you need to learn to KEEP YOUR STUFF CLEAN THE RIGHT WAY