Clean it once you see accuracy degrade. If you subscribe to the SH Online Training, Lowlight has a great video on cleaning. Give your rifle a really good, thorough cleaning and then note your accuracy. Shoot it until you start seeing groups open up, then you'll know at what point you need to clean it. I've heard of guys needing to clean every 100 rounds, some rarely clean their rifles,
Personally, I start to get the "cleaning itch" after about 250 rounds. I will wipe down the bolt if I get a bunch of sand/mud/etc in it, but I leave the barrel untouched for at least a couple hundred rounds.