Every couple of rides, unless it gets really filthy dirty. My roadie is a state but It was dark when I got back and the HA still hasn't fixed the bathroom light fitting. It needs a whole new one and they say that a qualified electrician has to do it. I am happy to let them but at the moment, I have no light in that bit of the flat and don't think cleaning in the dark, is likely to result in a good job. I'll do it tomorrow before taking it out for a ride.
If the bike comes back clean, after a ride, I clean the drivetrain and will maybe give the bike a wipe with a wetwipe. I'm not completely precious about them, I'm too lazy for that.