Aside from cleaning with saddle soap, oiling it every once in a while preserves the suppleness of the leather. Having a good cover for it helps as well.
You have to use a leather balm at least once a month on the whole saddle. Keep it somewhere dry where the temperature is constant, and neither too cold nor too warm. Wipe it with special soap applied with a microfiber flannel, then scrub gently with your flannel, then let it dry in the room. After it finished drying, apply the balm everywhere generously.
During transport, take care of your saddle. Don't dump it on the ground or against the wall... don't let your horse chew on it!! You can also use a saddle bag or cover to keep it clean and make it easy to transport without worrying too much.
When you ride don't use gear that will leave marks on the leather.
We also have a dehumidifier in our tack room
At my yard at work all tack gets cleaned after every use with water and saddle soap. It also gets piled once every one/two months
it depends on how much you use your saddle & the climate. don't clean it too often but don't let it get extremely dirty either. i like to wipe mine with a soft, dry cloth after each use. don't use water as it will dry the leather. condition it as often as it needs & oil it once a year. best way to make it last is don't let it get wet, keep it in a stable climate, and keep the dirt off of it.