Do not capitalize every thing because if you do the person will think you are being rude.
Always include your name because if you do not the person will not know who it was by.
Do not use text-speak because it will go directly to your trash bin.
If your writing a teacher about a project of assignment make sure you give some background information.
Have a good tone because if you do not the people might think you do not care.
Have good topics for email or the people will get bored and wont care about your email.