To wipe dust off the outside of the lens, it's okay as long as the cloth is very clean. If you're trying to clean the inside, use an air blower -- NOT the compressed air cans from Office Depot. Giotto's Rocket-Air Blower is recommended more often than others.
your best bet is to go to www.bhphotovideo.com and order one of their lens cleaning pens.
I just ordered a new one myself. they work great, and also, always wipe in a circular pattern starting from the middle and work your way out to the edge.
Do not just use any clean rag, you will scratch the daylights out of the lens.
Also, an important note, once you have your lens clean, buy a uv filter for your lens. its just clear glass, and will protect your actual lens, and also keep it spotless.
What they said, but always use a blower on your glass before using a cloth to blow away any chunks so they don't get caught in the cloth and scratch. Giotto Rocket Blower is preferred because it blows air out one end and sucks it in the other. That way you're not blowing dust out and sucking it back out the same hole.
gary