gilest.org: Clarity hacks
Principle #11: Message Organization—Attaining Critical Clarity
Drew Eric Whitman • Cashvertising: How to Use More Than 100 Secrets of Ad-Agency Psychology to Make BIG MONEY Selling Anything to Anyone (Cashvertising Series)

Ruthlessly edit your remaining text copy. Simplify concepts and cut to the chase.
Maura Ginty • Landing Page Optimization: The Definitive Guide to Testing and Tuning for Conversions
As for how to write well, here's the short version: Write a bad version 1 as fast as you can; rewrite it over and over; cut out everything unnecessary; write in a conversational tone; develop a nose for bad writing, so you can see and fix it in yours; imitate writers you like; if you can't get started, tell someone what you plan to write about, the... See more