As it happens, I’m wearing my (recently cleaned) Clarks Desert Boots right now. They’re the ‘Wolf’ colour (taupe to anyone else).
I do the following:
1) Stiff bristles on the suede brush to remove mud/dirt/dried in blemishes.
2) Suede shampoo all over and leave to dry for 30 mins.
3) Suede cleaner block (like an eraser) to remove any marks that have survived.
4) Scotch Guard (other waterproof treatments are available etc etc) and leave to dry for 30 mins.
5) Raise the nap again with the soft side of the auede brush.
I’ve done this to my desert boots 6 or 7 times and they still look near enough immaculate after 3 years regular use.