use 11 or 12 point font
If you use a small font, its just a bit extra effort for the reader, and you should always be making your reader’s job as easy as you can. On the other hand, if you use a big font, readers tend to feel your trying to bully them and they don’t like it. In any case, big text isn’t a natural read and people don’t find it comfortable to read
the danger of highlighting
/you may be tempted to highlight some words or sentences to increase the change of getting the most important information over - but remember, the real target is to get teh whole email read. The risk you run is that the highlighted parts are the only parts that get read. If these are the only parts you want your reader to see, why did you write the rest?
don't type all in capitals
Many people know this one already, but not all. Typing all in capitals IS CALLED SHOUTING. The reason its so offensive is that the message you’re giving to your reader is that they are so low value to you couldn’t even be bothered to turn off the caps lock before typing them a message. This subconcious message your sending to your reader is far more powerful than whatever message you were trying to get across with the words you typed. Its rather like the difference of body language vs spoken language, literally the difference between speaking to someone and shouting at them.
type words out in full
Writing out a text on a mobile phone is fairly hard work, and its become common practice to miss letters and abbreviate pretty ruthlessly. When you write an email you normally have a full qwerty keyboard at your command. Your readers are valuable, respect them. If you make your reader feel low value, he’ll assume you regard the communication as low value. There’s always that big X button at the top of the screen, and its so easy to press.
keep the title relevant
People often reply to an email and raise different issues to those mentioned in the first message. After a few mailings, the subject matter discussed can quite different to the message title, which can make it difficult to find information later. There’s nothing from stopping you changing the title before sending on.
put your reply at the top
Some email programmes are set to a default which puts your reply below the message you received. Worse still, they can be set to start a new message and not show the original sender’s text at all.
People expect to see the new text at the top of an email, and previous text further down. If your text is at the bottom, it may well not be seen at all.
Both of these things are symptoms of settings on your email programme, rather than a bad choice personally made by you – but that makes no difference to your poor reader.