Magazine maintenance is something on which I am probably remiss. I reserve one or two magazines for non-range use and keep them loaded with defensive rounds. The others tend not to get cleaned very often, other than a wipedown of the exterior and follower with a patch spritzed in MPro7 cleaner. When I get back from a training course I will try to break down all the mags used in the course to give them a more thorough cleaning, since they will collect mud and crud from being repeatedly dropped on the deck. If too much dirt gets inside the magazine tube, it can bind up the rounds and prevent smooth feeding.
To pull apart a magazine, you push a punch or screwdriver through the hole in the floorplate to relieve the spring pressure, then push the floorplate off of the magazine. Make sure you watch out for the spring when the floorplate comes off, since not all magazines will retain the spring when the floor comes off (eye pro is a must here). Once the floorplate is off, work the spring and follower out through the bottom. Be on the lookout for a spring retention clip that sits at the bottom of the spring above the floorplate. When you have everything off, you want to clean the inside of the magazine tube, the floorplate, and the spring, and very lightly lubricate them before reassembling.
You also want to inspect the feed lips to make sure they are not dinged or bent, and I like to do this when I have all the magazines lined up for cleaning so that I can do a visual comparison. I learned a good lesson on magazine maintenance at my last course. We had someone had their gun go down with a live round jammed partially up the feedway. The round wouldn't move in either direction due to bent feed lips, and the round was far enough forward to prevent stripping out the magazine in a normal type 3 malfunction protocol. The on site armorer did some careful work to unstick the mess without causing an out of battery detonation--a live round stuck halfway up the ramp is never a good thing.