Rules of thumb for writing emails

What are your rules of thumb for writing emails? Do you have any? Or do you just write stream of consciousness every time?
Over time, I've come up with about 57 rules of thumb that I follow. But I want share just 5 really important rules of thumb with you today.
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1. Write like you speak
It took me a while to realize the benefits of writing more casually. As soon as you get rid of all the awkward phrases you learn in english class, your writing will instantly become more relatable.
If one were to adopt said writing style in ones own writing, one might engage one's readers more effectively <- do="do" example="example" not="not" of="of" p="p" to="to" what="what">2. Break down complex ideas into simple ones
Reading an email shouldn’t feel like you’re doing a really hard math problem. Before you click send do some extra work for your reader. Try rewording complex thoughts into simpler ideas. And please, for the sake of your reader, limit how many “hard” concepts you cram into each email.
3. Break apart long paragraphs and sentences

Take a look at how newspapers and magazines break up their content. Paragraphs in New York Times’ articles tend to be only one to three sentences long with white space between each paragraph. If you catch yourself writing long run-on sentences. Break. Them. Up.
4. Have one clear call to action per email
What do you actually want people to do? Follow you on twitter, facebook, and pinterest? Or do you want them to finish signing up to become a valuable user / customer?
Every time you add a choice to your email you increase the likelihood your reader will get confused and delete the email.
5. Use a P.S. for a second call to action
A secret among copywriters is that everybody reads the P.S. of an email. They may not read anything else you write, but for some reason people can’t resist the P.S. There’s a nice visual separation too so your content actually looks shorter. So if your boss insists you need more facebook likes, put it in the P.S.
I've found these rules of thumb help us tremendously and I hope they help you.
Share your great rules of thumb for writing emails in the comments
Sincerely,
Colin
P.S. No P.S. in this email. I just wanted to prove to you that you'd read it.