1. Proof read
No need to spend all day editing, but it's always good to take a quick read-over before you hit send. Don't let your message lose credibility or be misunderstood because of typos or weird sentence structure.
2. Share your main point first
There's nothing more annoying than an email where you have to read through a paragraph or more to find out what the purpose is. If your item needs further explanation, you can elaborate afterward. Is your main point an action item? Make sure to put your request and deadline right at the top.
3. Keep it simple
Don't blab for paragraphs about stuff that isn't relevant. Sometimes those huge emails are so overwhelming that people don't read what you have to say. If you have a lot to say, make sure you aren't repeating yourself and that you are saying it in the shortest, simplest way.