This game is not a heroic fantasy in vein of other popular RPGs, such as Dungeons and Dragons, or Pathfinder. Your characters have less gameplay resources available to them, survivability is low. Critical thinking, and open communication will be more successful than a carefully "power-gamed" character.
Your resources are tracked, time is tracked, and your character will live and die by their wits (including thinking quickly, and planning ahead!) more than their sword.
This game is a moderately to heavily procedure reliant, ongoing series of events that should be played over months or years at a time. It is akin to an Open Table game.
There should be a large cast of rotating players. There should be multiple parties. Players should come up with their own reasons to be in the world, with their own goals. They might not even start at 1st level with a goal beyond "become rich and famous" or "learn more spells". This game should be collaborative storytelling through open speech, collaboration, critical thinking, and of course, the toss of a dice.
The effects of characters on the world one night should be felt by others on later nights. If 2 groups want to explore the nearby "Haunted Caves", and one group on Friday night gets 3 rooms in, those rooms should be looted, and have much of it's denizens slain when the next group enters on Saturday night.
This game assumes that you are keeping strict time records, that you have a rotating pool of 4-50 players, that each player wants to play multiple characters who may or may not be in multiple parties. It assumes that resources are tracked, and that everyone understands that death is a dice throw away.
Many GMs these days have grown up being strict storytellers. Abandon this train of thought! A GM for ITD&TD can, and should, tell light stories, but they should be assuming the role of an impartial arbiter of rules, and a master of the world and should aid in the game going forward.
A GM will track time for the players, help resolve conflict, and put together adventures for the characters to go on. A GM should resolve rules, roll dice for non-player characters, and assume the roles of monsters or other beings the players get involved with. A GM should work with players to accomplish their goals, and not purposefully antagonize players. However, a GM should also strive for some limited realism. The world is dangerous, and foes will take all the advantages they can.
GMs, note that danger goes both ways. If you have a "big bad monster" guarding the treasure, and it dies because it failed 1 Saving Throw, that's how the dice roll. Essentially, you are subject to the same rules as the players.
As a player, you may have a character that you get attached to die unceremoniously in a dungeon. Sadly, adventuring is dangerous. Look at it as part of the story of the world, and be open to character death. Smart thinking, good planning, and some good luck go a long way in making it to higher levels.
Instead of thinking what kind of character you are going to play ahead of a session, wait to see what you will roll up, and start your process at the table. It is no fun if you think "I want to play a wizard" for 2 weeks leading up to the game, only to roll up a character with 8 Intelligence (Players will have some light recourse to create a character they wish to play, but you may not roll up what you envision your character being initially).
Each session should be episodic, and driven by players, rather than GMs. Players should decide a few days before the session starts where they want to go to explore, and by the end of the session should be back in town. If it helps, think about each session as a "board game night", where you will finish the game (the dungeon) before putting it back in the closet (heading to town) to play next week.
Or think of it like the popular MMORPG computer games. Game night is "dungeon night", and you are getting together 3-5 friends to plunge the depths of a dungeon. You won't log-out of the game mid-dungeon, but rather log out after you get back to town afterwards.