Start with the least aggressive method. For loose dust and light fingerprints, a clean microfiber cloth can help, but avoid rubbing hard because film emulsion scratches easily.

For more stubborn dirt, several answers recommend washing the film in lukewarm or hand-warm water. You can gently rub the film with clean fingers while it is submerged, which gives better control than a cloth. Using demineralized water can help reduce drying spots. A photographic wetting agent is preferable; a tiny drop of dish soap may work, but purpose-made film cleaner or darkroom film-cleaning products are safer choices.

After washing, remove excess water carefully with a very soft squeegee if you have one, then hang the film to dry.

Key cautions: avoid aggressive rubbing, especially on the emulsion side, and be very careful with stubborn glue or dirt because scrubbing can cause permanent scratches. If you clean film often, dedicated film-cleaning products and tools are available from darkroom/photo suppliers.