Get to the point.
Start with the important stuff.
Present concrete detail to convey an aura of reality.
Keep it simple.
Make it easy to read and easy to understand.
Keep it personal.
Only one person at a time will read your message. Not a group, not a committee, not a demographic.
Make it active.
Passive, abstract language does not hold the reader's interest.
Give away secrets.
Tell people something they don't already know. Make it worth their while to continue reading.
Don't be an acronymphomaniac.
Larding up your text with acronyms is a barrier to understanding and will cause your visitor to leave PDQ.
Use typography to make text accessible.
Don't hide your message in a gray wall of text. Subheads give your visitor a glimmer of what's ahead.
Be fresh, original, and interesting.
It's hard to do, but I can help.