Brooks saddles are famous for their comfort. Their leather breaks in over time to conform to the shape of the rider. After a few thousand miles of riding by one rider, the fit becomes very personalised. Brooks comfort may be difficult to believe, given how hard the saddles are. The older models are especially sought after; therefore, restoration is of keen interest to those who appreciate their superior quality. Restoration basically consists of making the leather suppler, so it can conform to a new rider's butt over time, and countering the leather's dryness.
Heat the saddle in the sun for a bit, if the season allows it.
Rub Proofide on the underside of the leather. This is a Brooks product, available at many local bike shops as well as online. According to Velo Orange, its advantage over oils is that it won't cause the saddle to become overly soft or lose its shape. Apply it two to three times per year to keep the saddle from drying out.
Rub pure carnauba wax paste (car wax without cleaners) on the topside to address cracking. Proofide isn't absorbed well on the topside.
Buff the top by just riding the bike.
Neats foot oil applied to the topside will turn a honey-coloured saddle dark brown, if that's the look you're going for. Other approaches include the following: slightly wet the leather before each ride (don't soak it), and ride it into a comfortable shape. This should take only a few rides. This technique is called "casing" the leather. Another approach is to soak the saddle in motor oil warmed by the sun for a few hours. This is a last-ditch effort, if the saddle is too recalcitrant for your taste and you need the saddle to fit you faster. If the saddle has disintegrated from repeated exposure to rain, you may need to re-cover it. Brooks will do this for around £50/$75 if you'll cover postage.
Don't overdo the softening or you can ruin the saddle. Apply oil or car wax to the topside once a year at most. Brooks doesn't recommend putting anything on the topside, so Proofide on the underside may be perfectly adequate to restore the saddle's suppleness and allow a new rider to reshape it. The leather does not absorb well in cold weather, so don't break in a Brooks saddle during the winter.