When I first got my saddle, I tried to clean and condition it after every ride. Now that it's a little more broken in, I still clean it after every ride, but I only condition it once a week. It is important to make sure you clean all of the saddle (even underneath) if you want it to stay nice and maintain quality. The bridle should be cleaned often as well, especially make sure the bit is cleaned after every ride so it doesn't get crusty!
I strive to clean and wipe down my tack after every ride. Many tack companies come out with their own brands of Saddle soap and conditioner for their specific tack. I tend to use that after rides and condition once every month to every other month. One of the greatest cleaning tools is a toothbrush (used or unused but don't use it again after!) as it can get into groves and crevasses in which a sponge cannot