If you want an old, dried out look use a dark brown as base colour and highlight it with a light beige. It makes a greyish leathery look.
Sakura\'s recipe for red leather is also good, though you could go a bit brighter with the highlights using VMC Red Leather if you want to. Depends on how you like the finish to be...
Old hard leather can be simulated by careful washes of VMC Smoke over most browns.
I fine that Chocolate Brown, Leather brown, Flat Earth, Beige Brown and Cork Brown (VMC) all work well together in painting leather.