If you notice any dust or dirt that has accumulated, it is best to use cans of compressed air, spraying from a distance of at least 10 centimeters should be able to blow away even the most stubborn dust. As for stains, fingerprints or other more persistent halos, it may be appropriate to use a microfiber cloth moistened with a little detergent for photographic lenses. Absolutely avoid the use of alcohol and non-specific chemical detergents because they could irreparably ruin the lens.