A quick run down of what I think is most useful and important:

Your goal in writing an email to me should be to write an email that makes me think about what you are saying, not how you said it. I should not have to spend a long time trying to decipher your email and you do not want your email to end up in my hall of shame for outrageous student communications.

Emails are forever.  Anything you put in email can be forwarded to someone else.  While most communications between students and professors are protected by FERPA and therefore not available to the public, I can and frequently do forward emails from students to teaching assistants and sometimes other faculty in order to coordinate the class.  In the case of behavior that violates the student code of conduct, emails may provide evidence of such behavior.  Do not write emails in anger.  Even though student/professor communications have some protection under FERPA, most email provided by employers is not private and employers frequently monitor employee email.  It is therefore a good idea to get into good habits now.


You may find these links discussing etiquette tips for emailing your professors useful:
All of these recommendations also apply to communications with teaching assistants.