If it's dark, mink oil to condition, if it's not, then it may darken the leather so avoid it.
If it's cracking or dry, neatsfoot oil, but again, may darken it so be careful.
If it's dirty, Lexol or Leather New saddle soap, clean wrung-out sponge, follow instructions.
Follow with a light conditioner, Lexol.
I prefer leather new to anything else for cleaning, and if you do it correctly you shouldn't need to condition it.