Use a supple rag or cloth and first dust the leather that you will be cleaning. Leather has a tendency to retain dust, so do not skip this step.
Remove any stains or spots by pouring a bit of rubbing alcohol on a cotton ball and wiping the spot away. If the spot does not disappear, then try some cuticle remover (not nail polish remover). Apply it in the same fashion as the rubbing alcohol, but leave it on overnight before wiping clean with a damp rag.
Use a good class of foam leather cleaner or saddle soap. Mix according to directions if necessary. Test the cleaner in an inconspicuous area first to make sure that the leather and the cleaner are compatible.
Apply the cleaner and rinse off if required. Many leather cleaners require that the soap just be buffed into the leather to complete the cleaning process.
Apply a quality leather protector after the cleaning process. Apply it evenly and generously. Keep your leather out of direct sunlight, which will cause leather to crack and fade.
Wipe over your leather with a damp cloth regularly. This will help to eliminate a buildup of natural oils.