Simply.
Get an old tooth brush with cheap black polish on into the welts and give them a scrub
A sylvet cloth, saphir polish. Apply polish to saphir cloth. Apply a small ammount to the cloth
Apply to shoe, when you feel resistance in the polish and a small amount of polish. What you are looking for is spirals to appear with no real excess water on the leather. If you feel scratching though. Stop rinse off polish with cotton wool. Clean the cloth, let it dry. Carry on
Bull into shoe until all gone…then repeat over and over again.
Once the mirror shine is there i then use soaking wet cotton wall with water and the tiniest bit of polish to make sure i get rid of any tiny scratches etc
But yeah find some movies, follow the above and youll end up with a good result. It just takes a long time and patience. The key is to resist putting tons of polish on in one go and balance with the correct amount of water.