If it is a hard, smooth, and shiny leather, you can use saddle soap to clean it a few times a year.

If it's softer and more grainy/textured, I'd probably use some of the other products mentioned - for my old soccer boots, I used mink oil fairly regularly to help with waterproofing and conditioning along with polish after every game to keep then looking sharp. I could usually get 2 or 3 good competitive seasons out of them with this maintenance routine.