Provided it's not stretched or torn, the best thing to do is ride it. The saddle and your butt will accommodate to each other over time. If the leather is dry, a sparing application of Proofide or SnoSeal may help, but don't go overboard -- this is a saddle, not a baseball glove, and it needs to be strong enough to support your weight. Softening products like neatsfoot oil are great for gloves or shoes, but can ruin bike saddles.