Along with knowing how to properly use a camera lens, knowing how to clean and care for one should be somewhere near the top of every filmmaker's list of skills. And we can all thank our lucky stars that this isn't a difficult thing to get right, so take a couple of minutes to watch this video by David Bergman of Adorama TV in which he shows you several ways to safely and effectively clean up fingerprints, dust, and other nasty stuff that is bound to accumulate on your glass.
Okay, this is pretty simple stuff. First, you'll want to use a blower to clear any small particles that may be on your lens. Make sure to hold your lens face down so any debris falls away from the glass. Next, use some lens cleaning solution and a microfiber cloth to clean up any fingerprints and smudges. Spray the solution onto the cloth, not the lens, and then begin wiping from the middle outward in a circular motion.
Of course, complete lens care is a bit more extensive than that. You may want to get your hands on some lens brushes to clear the lens body of any dust, sand, or dirt. (But don't you dare use them on your glass elements!) Canned air can also be used to do this, but just make sure the propellant isn't getting all over the place.
If you're not confident in your ability to clean your lens yourself, take that baby to a pro and they'll clean it up nice for ya.