If you've used the lens in a dusty environment, remove the dust from the lens using a soft brush. Wiping the lens with dust still on it could scratch it. Gently brush the dust from the middle of the lens to the edges. Then dislodge the dirt from the edges by holding the camera upside down with the lens glass pointing toward the ground, allowing the dust to fall toward the ground as you brush. Use a brush with soft bristles.
If you'd rather use something that doesn't make any contact with the lens, try a bulb blower or air bulb. It delivers a small puff of air without adding harmful moisture. Don't use your mouth or canned air. Blowing on the lens with your mouth could dispense saliva. Canned air can sometimes spray liquid difluoroethane, the liquid form of the gas used to deliver the air. Also, canned air can sometimes carry so much force that it can drive dust particles inside the lens housing, especially with cheaply made lenses. With a few gentle puffs from the bulb blower, you should be able to get most of the debris off your camera lens.
After removing dust, probably the best tool for cleaning a camera lens is a microfiber cloth, which is a soft cloth that you can find for less than $10. It’s made specifically for cleaning the glass surface on camera lenses and even glasses. It works well for removing smudges, with or without lens cleaning fluid, and a microfiber cloth can clean other parts of the camera, too. Start wiping gently in the middle of the lens, using a circular motion as you move toward the edges of the lens.