I really enjoyed reading this blogpost and have shared it with my students; I’ve also shared with other advisers to share with their students. The opening paragraphs:
Every semester, I see the tweets and Facebook posts. My professor friends, they are annoyed. Their students do not know how to write emails, they say. What they really mean is that their students don’t know how to follow the conventions of email etiquette in the academy. I used to be exasperated by student emails too. Until I realized that there was a simple explanation for why they didn’t know how to write them — they’ve never actually been taught how.*
But now, clueless students have no excuse, because they can read this post. Profs, share it with your students. Students, share it with your friends. Or don’t, and be the one person in the class your prof enjoys receiving email from.
10 Elements of an Effective, Non-Annoying Email
Here’s a template you can follow in constructing your email to a professor. Each element is explained further below.
Dear  Professor  Last-Name ,
This is a line that recognizes our common humanity .
I’m in your Class Name, Section Number that meets on This Day . This is the question I have or the help I need . I’ve looked in the syllabus and at my notes from class and online and I asked someone else from the class , and I think This Is The Answer , but I’m still not sure. This is the action I would like you to take .
Signing off with a Thank You is always a good idea ,
I recommend reading the whole thing at https://medium.com/@lportwoodstacer/how-to-email-your-professor-without-being-annoying-af-cf64ae0e4087#.gpusikv4s