Matthew Butterick, in the first chapter of his wonderful “Butterick’s Practical Typography” book:

This is a bold claim, but I stand be­hind it: if you learn and fol­low these five ty­pog­ra­phy rules, you will be a bet­ter ty­pog­ra­pher than 95% of pro­fes­sional writ­ers and 70% of pro­fes­sional de­sign­ers. (The rest of this book will raise you to the 99th per­centile in both categories.)

All it takes is ten min­utes—five min­utes to read these rules once, then five min­utes to read them again.

Solid advice, and it only gets better from here. If you care at all about typography, this book is a must-read.

Via Chris Gonzales.