Since the lens is very sensitive to pressure and sharp surfaces, you need to use a very soft brush for the cleaning. The brush should have very soft bristles. Use this brush to remove the trapped dirt from the crevices around the lens. Since a cloth cannot reach into these crevices, the brush bristles will be able to do so.
Take a microfibre lens cleaning cloth. This cloth is usually available at optic stores and is lint free to reduce the impact with the lens. Make sure that the cloth is chemical free. Breath on to the lens surface so that it is moist. Fold the cloth neatly and use it to wipe the lens in a circular motion.
For effective cleaning, pour a few drops of lens cleaning fluid on the cleaning cloth. The cleaning fluid should be methanol or alcohol based; will generally be available at optic and digital stores. Wipe the lens in circular motion with this cloth. This will remove any persistent stains on the lens through the cleaning properties of the fluid specifically used for this purpose.