Considering the rust I've found in the mag tubes of old shotguns, I'd say that most people don't clean/lube the mag/follower

I'm starting to use nylon brushes as a substitute for endless patches in rifles. I only use steel on old milsurps that have layers upon layers of crud in them.

For shotgun, most all I do is run a couple oily patches down the barrel after shooting and wipe it down. no more than once per year I'll soak choke tubes in a jar of Eds Red with a whole lot of acetone added to melt the wad plastic out.

I don't take apart the receiver for cleaning unless it's dead nuts easy to do - I won't strip an Auto 5, for example, and the old remington 10 I picked up this year just had the wood taken off and the receiver soaked in a pickle jar of Eds Red (no acetone) for a few days, and cleaned as best I could without further disassembly - it runs and the nooks are lubricated.

Lots of good tips above that don't need repeating