The DM-Friendly Initiative (DMFI) has published two self-teach tutorial modules on NWVault designed to teach basic DMing skills. They can also be helpful for more experienced DMs as a comprehensive review of the DM client (along with maybe presenting a new trick or two).
DMFI 101: So You Want To Be A DM (for NWN / NWN:EE)
DM 101 for NWN2
DM training modules for NWN and NWN2
Re: DM training modules for NWN and NWN2
Links have now been updated for the new Neverwinter Vault.