Remove loose grit first by blowing it off or brushing it away, so you don't drag it across the glass. Then clean off smudges and fingerprints with a tool or cloth made for optics, working from the center outward. Skip shirt tails and paper towels, which can scratch lens coatings.
A cloudy film is usually skin oil, a fingerprint or dried moisture. Clear loose dust off first, then gently work the film off with a lens cleaning tool or optics cloth instead of rubbing hard. If the haze is inside the optic rather than on the glass, that's a warranty question for the manufacturer.