Dont let your leather get to soft or it could rip.
I use synthetics, so I wash them every time, which is easy cos I just scrub it and towel it dry. I dont wash my saddle tho, just wipe it if it has sweat on it. And any girths or breastplates get rinsed and hung up to dry.
My show saddles and bridles get polished after they are used or otherwise every couple of months to keep it moist. And I use a black polish so that it keeps the leather ( I use all black tack) looking like new.