"The best way to keep lenses and filters clean is not to get them get dirty in the first place! This may sound trite, but every cleaning carries with it a very small risk of causing problems. The major problem is the risk of scratching. Scratching occurs when something harder than glass (or the optical coating) is rubbed on the lens. Of course lens cleaning tissues, cloths, brushes and fluids aren't harder than glass, but dust and dirt may be. Hardness can be measured on the Knoop scale. For our purposes here it doesn't really matter what the numbers mean, but it is important to know that a material with a higher number will scratch a material with a lower number."This is such a short and correct article that it should be required reading for all. I had sort of been following its advice already because much of it makes sense but I have seen a number of other people that just wipe their lenses with their shirt or worse, their thumbs. This describes the process that should be used and justifies the steps.