Writing Clear by: Justo Almodovar

According to Edward T. Thompson who is/was the editor in chief of Reader’s Digest there are only three basic requirements to writing clearly:
1) You must want to write clearly
2) You must be willing to work hard.
3) You must know and follow some basic guidelines.

These basic guidelines that Mr. Thompson mentioned are:
1) OUTLINE WHAT YOU WANT TO SAY meaning that you need to make sure that you know what you are going to say and know when you are going to stop.
2) START WHERE YOUR READERS ARE which means keep it simple and do not write at a higher level than where your reader’s knowledge is about the subject.
3) Don’t use words, expressions, and phrases known only to people with specific knowledge or interests, basically AVOID JARGON.
4) USE FAMILIAR COMBINATIONS OF WORDS; be careful because the term familiar combination of words does not mean incorrect grammar.
5) USE "FIRST DEGREE" WORDS which are words that bring an image to your mind almost immediately such as: face, stay, or even book.
6) This is where the outline in step one helps you drastically because you want to make sure that you STICK TO THE POINT.
7) Last but certainly not least BE AS BRIEF AS POSSIBLE because whatever you write, shortening condensing almost always makes it tighter, straighter, and easier to read and understand.

Sources:

http://www.harmonize.com/probe/aids/manual/Write_cl.htm
http://www.digital-rights.net/images/writing.gif