How Often?
Not as often as my friends think I should! Sadly for most of them, they can't outshoot me and have a hard time telling me that "you'll loose your accuracy!"
Seriously, it depends on how ambitious I am. Before a match, I always clean my rifle. Or at least clean the bolt and carrier and trigger group (it's an AR-15).
My Marlin, my .22s and others, I get to when I get to. Usually it's a lazy-afternoon thing, or if the .22 seems kind of grungy. The Marlin will run well even very dirty, and accuracy doesn't seem to matter either way.
I don't run brushes down the .22 bores and I rarely use solvent. Something I picked up from smallbore shooters, who very rarely clean their rifles.
Now my Glock, I clean every 500 rounds or 3 months, whichever comes first. Sometimes it's 3 month, sometimes it's 500 rounds. And sometimes I wait 3 months when I know I'm over my 500 rounds!
My opinion, most firearms are more durable and more reliable than most people think and don't generally need the white-glove treatment more than twice a year or so (more often for anything I'm using for matches or "non-range").
Of course, when I feel I need to give something a good cleaning, I go shoot blackpowder.