Start with the gentlest method first.

1. Blow off loose dust first using a bulb blower. This is important because wiping dust or grit across the glass can scratch the lens coating. Avoid canned air. If you use your breath, be careful not to add moisture or residue.
2. Wipe with a clean microfiber cloth if any light marks remain.
3. If the smear is still there, use a lens cleaning wipe or a lens pen made for optics. These are designed for coated lens surfaces and are commonly used for front elements.
4. For more stubborn oily marks, use a small amount of optical lens cleaning fluid and then wipe with microfiber or lens tissue.

A few tips:

• Always remove particles before wiping.
• Use a clean cloth or fresh wipe so you don’t reintroduce grit.
• Clean in a relatively dust-free place.
• Don’t soak the lens; use only enough fluid to clean the surface.

For a little dust and a translucent smear, a blower plus microfiber or a lens wipe is usually enough.