I would like the DMG to be about 10% advice for new DMs (this should be chapter one), 10% rules that players don't need regular access to, and the rest a grab-bag of ready-made tools for the DM who needs to whip something up on the fly. I'd like to see the following chapter headings, in no particular order:
- Traps and Puzzles
- Social Scenarios
- Magic Items and Treasure
- Wandering Encounters
- Lairs
- Downtime Activities
- Mass Combat Scenarios
- Domain Ruler Scenarios
- Basic Bestiary