I run the follower up and down a few times with my thumb. If the motion is smooth, I wipe the outside of the mag with an oily rag and move on. If the motion feels gritty, or if it binds, then I'll clean it.
I find taking most mags apart to be pretty difficult, so I have a plastic "tupperware" that I put mags in, then soak them in Hoppes #9. I have a special bottle of Hoppes that I only use for soaking. Afterwards, I use a coffee filter to strain the solution back into storage.
I'll dump the mags in when I start cleaning gune. Every so often, usually after I finish a gun, I'll take the mags out, run the followed a few times, then toss 'em back in. Once I am out of guns, I pull the mags, shake them off, then leave them to drain on a bed of paper towels while I start cleaning up. By the time I get most things put away, the mags are ready to go back into storage, clean and ready to be abused again!