One of the biggest pitfalls for novice game masters of any tabletop RPG is knowing how and when to say no to players.
Learning to improvise in Dungeons and Dragons: How to salvage a session when your players are Chaotic Neutral
Tabletop players are unpredictable -- that's what makes Dungeon Mastering fun, ultimately.
Here's a little secret -- I don't do a lot of formal planning for running my D&D games.
Every Dungeons and Dragons Dungeon Master has been there.