I walk through the boggy muddy fields up to my calves in mine and just hose them clean, always have warm dry feet!
Only actually cleaned them once and they come up like new!
Rub E45 cream into them. Cheap to buy and excellent for you hands too, readily available from supermarked to chemists. Works a treat. Was recommended to me by the firm who made my riding boots, now used it on all my boots, certainly helped prolong the life of my Ariats.
I have used dubbin on mine when they were looking a bit tired.
Always good to give them some protection b4 you use them like any leather products to prolong their live, but not essential - they are waterproof without any protection.
I dubbined mine during the summer and have worn them all winter with just a hose off at the end of the day.