Munin
First Post
It is a good for DM s to continually try new things nad improve their skills.
This can't be overstated. You've got to stay one step ahead of your players. If you don't push yourself, your game will grow stale over time.
On a more practical level, I find it helpful to ask the players what they intend to do next session (if I don't already know) and work from there. If it involves a dungeon-type environment, make sure you read it over so you can anticipate any problems that may arise.
If it involves heavy roleplaying, add something that has NOTHING to do with the players.
When you have extra time, work on adding depth to your NPCs.
Establish side plots that will draw your players into your campaign and involve them in it.
Take your player's character sheets after each session and go over them. The object here isn't to exploit their weaknesses (which is exactly what they'll think), but to look for obscure skills, feats, or unused abilities that you can include in future sessions.
Change one thing about every NPC between adventures.
Since you're going to run the Shackled City, make sure you read the fine storyhours on this website. Mine them for ideas.