Most scratches on optics come from improper cleaning practices. Tiny particles of grit get on the lens from dust. When you clean with a cloth, no matter how soft the cloth is, your scrubbing that grit that is already on the lens into the coatings and that silica grit is hard stuff.
Go to a professional camera store and look into camera lens cleaning supplies. We have a few hundred in a sight, they can have thousands in a single lens. Get a good lens puffer and soft brush. Use these first to remove grit from the lens. Hold the lens where gravity will cause the dust and microscopic grit to fall away from the lens as you puff and brush. Then use a lens cleaning solution approved for optical coatings on fresh uncontaminated Q-tips to clean oil from the lens. Last use camera lens approved lens cloths to polish any streaks from the lens. Lastly, clean at home in your filtered air of your home. No matter how tempting, try not to resort to cleaning in the field. Live with smudges till you get home.
