How to email a teacher/professor, the proper etiquette guide

When emailing a teacher, instructor or professor, there are a list of things you should and should not do do to not get on your instructors bad side. 

Things you should do when emailing your instructor:  Do...

1. Include a relevant subject.  Something like, question from "name here", or student in mwf 11am class.
2. Make sure you address your instructor appropriately, it is accepted practice to begin an email with Hello Dr. so and so (if they are a professor or a doctor).  You can always use "Instructor so and so" and should avoid using Mr. or Mrs. because using Instructor or Dr. shows more respect.  Even if your instructor isn't a doctor, they will get a thrill out of being called doctor especially if they are a graduate student :) .
3. If it is the first email you have sent to him or her you should introduce yourself and identify the class that you are currently taking from the instructor.  For example, if you are in the Monday/Wednesday?/Friday class at 11:00am, you could say something like: My name is  I am a student in your mwf 11am class.  
4. Get to your point quickly.  If you want be friendly, keep it to one sentence.  Your instructor does not want to read about the weather, current events, or hear about your life.
5. Similarly, your point should/could be related to your title. If it isn't, you should rethink the purpose of the email.
6. Double check your email to make sure it is not longer than a few paragraphs with a few sentences per paragraph.  If you need to communicate more information than this to your instructor you should really visit them during office hours.
7. Finish your email with something like: "sincerely, warmly, best, thanks" and include your name.

You definitely should not do the following:  Don't....

1. Leave out your name in the entire email.  It should either be in the subject, or at the end of the email so that your instructor can identify who you are.  It is very frustrating to get a frantic (or even normal) email from a student and then not be able to act on it because you have no idea who sent it!
2. Leave the subject blank/use an irrelevant subject.  This immediately turns of the instructor or makes the message look like SPAM.
3. Go on and on about your personal life, or irrelevant topics.  Your instructors probably get anywhere from 5 to 100 emails a day from students depending on the number of classes they teach and the size of the classes.  They want to get through their emails quickly, without having to wade through garbage.