If they’re dirty, run them through the washing machine or replace them.
Use a soft cloth or a brush to remove any grime that may be stuck to the shoe’s leather surfaces.
Mix a solution of warm water and dish soap, dip a soft cloth into it, wring it out and wipe the exterior surfaces of the shoe.
Use a second clean, damp cloth to wipe off the soap. Dry with a towel. Warm, soapy water will also remove water stains and scuffs.

Apply leather conditioner to protect from stains and to add shine. You can buy a commercial leather conditioner or make your own by mixing 1 part vinegar to 2 parts linseed oil. Apply to leather, let sit for about 15 minutes and buff with a soft cloth till the leather shines.
Let your shoes and boots dry in the open air. Don’t put them in the sun or by a heater, as this may cause the leather to fade or crack.
Grease or Oil
Ink
Scuffs
Other Stains
source : https://www.diynetwork.com/