Before you learn how to clean your hats by hand, keep a few things in mind.
Always read the instructions tab carefully. You will find it usually attached or sewn onto the headband. The instruction tab will show you the proper way to clean the hat without causing any damage to it.
There are different types of hats, and each hat will have a unique way of cleaning them. The sweatband is often the part of the hat with the most stains. So that is always a good place to start.
For cleaning a fabric sweatband, always use a soft brush and a mild detergent. Fold the band down and scrub it using the brush and detergent. After that, wipe it with a clean cloth dipped in water. Leave the band out to dry.
For cleaning a leather sweatband, get a good leather cleaner to remove the stains and odors. Follow the directions given on the package to clean the hat, and after it is done, leave the hat on a clean area to air dry. After it is done drying, use a leather conditioner to protect the sweatband from getting worn out.