Don't weep about HTML links etc., they are not an excuse for some other format.
Remember to break your message into short paragrphs. Handle exactly one topic in each paragraph.
Put a blank line between paragraphs. This makes it easier to read.
Avoid excessive quoting. Truncate redundant crap!
It's a good habit to try to write self-contained e-mails and delete all quotes.
This helps also to clear your thinking.
Also, it's a good indication for others that you have actually understood what you write about, since you are able to express it with your own words.
If you quote, place your own text below the quoted text. Do not TopPost!
When quoting, use quote character ">", do not embed your own name within the text. You'll ruin the flow of the text.
Always revise To: and CC: fields. Don't use Reply All unless there is a very good reason.
Write proper sentences:
End questions with a question mark.
Start every sentence with a capital letter.
Use commas and semicolons when needed.
Use either Finnish or English but not both.
Use simple sentences. You are more likely to get them right.
If you don't know how to write, then be QUIET for heaven's sake.
Do not write in passive, especially not in English. Be always exact on who does what!
Use passive only when you deliberately want to be fuzzy and only if you know how to use passive in English. Most of us do not know.
Choose appropriate Subject: line.
You are also allowed to change it when replying. "HEY READ THIS E-MAIL!!!!" is not a good subject line.
Think hard before sending any attachments.
Don't flag all your e-mail as important.
After finishing writing, before pressing the send-button, read your mail once again to double check that you have explained your point clearly and others understand your message correctly.
Is there any room for misunderstanding?
Did I miss explaining certain issues that others do not necessarily know?
Don't send "Why don't you respond to my e-mail?" e-mails.
Don't send "Thank you for responding to my e-mail!" e-mails.
Don't start back-paddling when you have made a mistake, and don't start your e-mails with silly stories about your insomnia, marriage problems, etc.