Give them a good wash out with warm ( not hot) water or get the garden hose in them ( or Warm then blast with the hose).
Stuff with newspaper after they have drained and leave them to dry indoors ( not too near any direct heat. Change the newspaper once or twice then just leave until dry.
Oil them up when dry and off you go!
Some good suggestions so far. Another is to fill them with a strong saline solution (warm salty water), leave them for a few days, then thoroughly rinse them. Allow to dry naturally (don't put them anywhere near a radiator or fire, remove the footbeds and don't stuff with newspaper). Once dry treat them with a good wax, I prefer Sno seal if you can get it. And they should be as good as new.