How to ask for tech help, 2013 edition

I first tackled this subject a few years ago, then updated it back in 2011. Given the recent batch of incomplete, incomprehensible, and/or inappropriate e-mail I've received, this seems like a good time for another update. See, every month I get loads of letters from users seeking help with a computer problem. Time doesn't permit me to answer them all (and I'll admit I don't always have an answer), but I do my best. Consequently, I need you to do your best as well. That means asking the right qu...