In the photography forum, I've been seeing some threads on lens cleaning that recommend lens tissues. This is a cheap and convenient way to do it, but it is also risky. Tissues trap dust and grit between lens and tissue and it is all too easy to scratch the lenses. Some lens tissues, meant for eyeglasses, are actually mildly abrasive and can scratch coated lenses with no help from trapped grit. Microfiber lens cloths are safer, but still not 100% safe. So how do you do it?

Well, first you go over it with a blower and lens brush, to remove as much grit as possible.

Next you are going to need some solvents. Commonly used solvents used in camera restoration (and lens cleaning) are:
1. denatured alcohol, used to remove tar (from cigarettes, or pine pollen) and detriorated light seal material (sometimes found stuck to rear lens elements). Do NOT use rubbing alcohol; it will work, but it is not a benign solvent and it can attack some balsam cements used to glue lens elements together.
2. naphtha (Ronsonol lighter fluid), used to remove grease and oils (naphtha is REALLY good for fingerprints).
3. distilled water, used to remove everything else.

These are all benign and won't harm your camera if you just keep them out of the electronics and don't actually SOAK the camera in them.

4. One other special solvent: a 50/50 mix of hydrogen peroxide and ammonia, used to kill and remove lens fungus.

Then you get a big box of Q-tip cotton swabs. Dampen a swab with your solvent of choice, and start in the center of the lens, working outward. A little solvent goes a long way, so you want your swab to be damp, not wet. Use gentle pressure, not much more than the weight of the Q-tip. Don't scrub, but let the solvent do the work. Twist the swab as you go, so that a fresh surface is kept in contact with the lens and any grit is lifted away from the glass, not rubbed against it. You'll go through quite a few Q-tips. I generally go over my lenses two or three times with each solvent.

When you use the naphtha, you may notice a haze forming on your lens as it dries. Don't panic; this is a GOOD thing. The haze is oil and grease that has been hydrolized (made water soluable). The naphtha itself leaves no residue. When you go over it with the distilled water, it will remove the haze.