A safe, effective approach is to use a blower or soft brush first, then only use a cleaner if needed.

A common kit is:

• Rocket blower / soft brush: removes loose dust first, which helps avoid rubbing grit across the glass.
• Lens pen: popular for field use; convenient and effective for light marks after brushing.
• Wet cleaner + disposable wipes/tissues: useful for stubborn smudges or oil. Answers mention optical cleaners such as ROR, Eclipse, or Pancro, used with disposable lens tissues or lint-free Pec-Pads.
• Microfiber cloth: handy in the field, but keep it clean since reusable cloths can pick up particles.

Pros:

• Blower/brush is the safest first step.
• Lens pens are compact and easy to carry.
• Proper optical cleaning fluid with lint-free disposable wipes cleans oily residue well and leaves little residue.

Cons:

• A lens pen may not remove all smudges.
• Reusable cloths can trap grit if not kept clean.
• Canned air is mentioned by one user, but a hand blower is generally the safer choice for lenses.

Best practice: start dry, clean gently, and only move to fluid when dry methods don’t remove the mark.