Brevity

How many times have you received an email with the text "FYI", followed by a long, long, long email thread that is impossible to follow? How many times did anyone send you a very long email that by the time you reached the end, you have lost the point of the email?

How many times did someone try to explain something to you on a meeting and that person took so long to get to the point that you lost interest in the thing that person was trying to explain?

Brevity.

We are busy. We lead lives full of noise, be it social media, emails, spam, offers, ads, commercials, and just people trying to grab our attention. No. Stop. Strive for the fewer words possible that can effectively make the point.  

When you write that email, think. If it's to someone new, introduce yourself in one sentence. Then explain the reason of the email, the problem and what you need in one short paragraph. Say thank you and leave it there.
If you are forwarding something, and you expect the person to act on that, write a summary, short, indicating the issue, and what you need from him or her. Simple.
And if you are in a meeting, don't waste people's time. Omit the powerpoint, if you can, or have a one or two slides deck. Make it a point to explain the thing you need, and why these people are in the meeting in the first 10 minutes. Then, the rest of the time is for them to ask questions. 

Brevity.