Front elements are coated, and coatings scratch. Almost all the damage people do to lenses happens while cleaning them, which makes the order of operations more important than the products.

The principle: remove loose dust before anything touches the glass. A grain of sand under a cloth is sandpaper.

Blow the dust off first

Use a hand blower — a rubber bulb, not canned air, which can spit propellant onto the glass. Hold the lens face down so what you dislodge falls away rather than settling back.

This alone deals with most of what is on a lens most of the time.

Brush what the blower missed

A soft lens brush, used lightly, takes off anything still clinging. Do not use it on a lens you have already wetted, and do not touch the bristles with your fingers — the oils transfer.

Only now, wipe

For fingerprints and smears, a drop of lens fluid on a microfibre cloth or a lens tissue. Put the fluid on the cloth, never directly on the lens, where it can run into the barrel.

Work from the centre outward in a spiral, with light pressure. Finish with a dry part of the cloth.

What not to use

Shirts, sleeves and tissues — all carry grit.
Canned air — can spit propellant and drive dust into the barrel.
Household glass cleaner — the ammonia in it attacks coatings.
Breath — deposits more than it removes.

The part people forget

Keep the rear element cleaner than the front. Dust on the front of a lens is almost invisible in a photograph; dust on the rear element is much closer to the sensor and shows far more.

A cap on both ends whenever the lens is off the camera does more for image quality than any amount of careful cleaning.