1. Read. I thought I'd start with the most obvious one. Read. Read everything. EVERYTHING. Novels, biographies, books about neuroscience and The Bay of Pigs, National Geographic magazine and Writers Digest, People Magazine and The National Enquirer, the dictionary, the thesaurus, author blogs, artist blogs, tech blogs, old archived newspapers and online newspapers, your old history textbook, the phonebook and the back of your Waffle Crisp box. EH.VREE.UH.THEEN.GUH.
2. Watch. This one is a fun one. And easy, given stuff like YouTube and *ahem* watchseries.com. There's so much out there. Documentaries, black and whites, cartoons, sitcoms. I have this weird dichotomy with TV were I feel like depending on the show, I learn more and am more creatively inspired by watching than by almost anything else, or it relaxes my brain and shuts it off more than anything else, which, given the fact that it can take hours for me to fall asleep sometimes because my brain won't shut up, can sometimes be refreshing. Anyway, I love watching awesome story shows, everything from The Office to House to Downton Abbey to Frasier to Person of Interest to Lost. All of those give me so many character and story ideas and I love it. Then there's also all the Discovery and History channel documentaries that honestly help me remember and learn cool new facts better than anything else. Or there's, you know, Johnny Bravo and Phineas and Ferb that shut my brain off when I need it.
3. The Interwebs. I suppose this is sort of a combination of the first two, but you can teach yourself basically anything through the internet nowdays. My brother is teaching himself computer programming via instructional videos on YouTube. Wikipedia can give you a basic run-down/background of pretty much anything ever. You can teach yourself a new language, find recipes, guitar chords, anything. Pick something you want to teach yourself, and learn.
4. Exploring. I wish this one was more natural for me than it is. I love learning stuff at my bedroom desk, but sometimes I go outside and the sun is bright and I feel like I'm Frankestein's monster coming out into the world for the first time or something. I should probably work on that. It's good to get out and explore and experience things first-hand. Go to museums or art shows. Take pictures, look at birds and bugs, go fishing. All things I should do.
5. Community Resources. In most places it's pretty easy to find something like night-classes or workshops or clubs that can help you learn what you want to learn, or just stretch your mind. I'm lucky enough to live in a college town that I should probably be taking much more advantage of then I am. The classroom setting is sometimes just awesome, and even if we're all gradumicated there's still that option sometimes.
So there you have it. Ways to keep your brain from atrophying. Anything else you would add to this list?