A collection of individual articles touching on how to run tabletop RPGs. Dig in, GMs!
Downtime (WotC Unearthed Arcana)
What Is This Book About? (Wikipedia Method)
What's A Class?
The Social Beast: Choosing a Table
What does it mean to DM?
Why do I DM?
See also my "d100 Dungeon Master Tips" Critiqued weekly series (updating each Friday!), which deals primarily with GMing techniques!