Below are linked some of the core resources for DMs from the DM-Friendly Initiative (DMFI) and the general NWN community. Additional recommendations for the list are welcome.
DMFI 101: Enhanced Edition is a tutorial module that shows how to use the core functions of the Neverwinter Nights: Enhanced Edition (NWN:EE) Dungeon Master (DM) client, as well as demonstrating some common uses of the DMFI Wands and Widgets. After completing this module, players will have the skills necessary to successfully run a multiplayer NWN session as a DM. It also can serve as a refresher for more experienced DMs.
DMFI 101: So You Want To Be a DM is the original, Neverwinter Vault Hall of Fame tutorial module for NWN-1.69.
DM-Friendly Modules on Neverwinter Vault have all been certified as playable and meeting the standard for DMs to be able to run "out-of-the-box" using the accompanying documentation.
DMing in a Persistent World Environment is a revised and updated guide to techniques for effective DMing on a PW. The contents cover a number of conceptual and practical issues and were originally based on a discussion at the old Bioware DM-Friendly Initiative (DMFI) Guild forum.
Creating and Running a Neverwinter Nights Campaign walks through the process of building and DMing your own campaign, including a number of other valuable resource links.
Lazybones' The Neverwinter Connections Community Guide to Dungeon Mastering is the original 'Old School' guide with a wealth of information that is still relevant today.
For module builders, the DMFI Multiplayer Starter Mod for NWN:EE has the DMFI tools pre-installed. The mod and its documentation should be accessible for novice builders, while at the same time being useful for more advanced ones who want to do their own modifications and extensions. Different resting systems and bleeding/death/respawn options are included, allowing customization of the in-game experience. In addition, DMs will be able to modify which rulesets are being used while in-game.