This paper from the Asian Development Bank (ADB) outlines the rationale for using plain English and describes a number of strategies that can be used to ensure documents are written clearly and concisely.
"Plain English—or plain language—is a message written for the reader in a style that is clear and concise. It is quicker to write, faster to read, and puts messages across more often, more easily, and in friendlier ways. Using plain English, writers should
- Select simple words.
- Make lists.
- Keep sentences short.
- Refrain from giving unnecessary details.
- Cut down on jargon and use defined terms sparingly.
- Discard superfluous words.
- Reduce nominalizations.
- Avoid weak verbs.
- Use the active voice with strong verbs.
- Be specific rather than general.
- Write personally, as if you were talking to the reader."