There is a subject line. Use it. The subject line is there for you to quickly summarize what the email is about. Take a few seconds and make it meaningful. “Minutes from the 7/13 meeting – no response required” is much better than “Last meeting.”
Keep your emails short. People receive a lot of emails these days. Don’t waste anyone’s time.
Be polite, dammit. Didn’t your mother teach you to say “please” and “thank you”? Being polite in an email goes a long way. Polite words are a great way to overcome the lack of body language present in an email.
Open and close. Start with a salutation and end with a valediction. “Hi, Amy.” “Sincerely, Adam.” Would you start a conversation with someone without greeting them first? Would you leave without saying goodbye?
Keep the signature short and professional. This is one of my pet peeves: the extra-long email signature. Keep it to five or six lines. No need for Chuck Norris quotes. You probably don’t really need those mailing addresses or fax numbers, either. I prefer name, website, social media and phone number.
I think that these are pretty simple. Without much effort at all, you too can stop being an email asshole.