While I never GMed Blades in the dark I have some forged in the dark XP and GM an old game about thieves a while ago, so I may have some pointer

Mechanics

forged in the dark is IMO at the sweet spot between rule light and rule heavy, while the core rule are simple, the stress mechanic, the position/effect, and the special playbook action adds a certain layer of complexity, do not advertised it as a rule light game it’s not.

Another important thing, ask the player to roll the f… dices. As a GM, I tend to skip roll for “common action” that the player would be able to do no matter what. In Forged in the dark, “everyting is a clock” that you fill with failure/success. So rolling the dice is what make the games move forward (and the whole partial failure means that the dice result matters). In general I keep a large macro clock the plot thicken/alarm level when I’m getting rid of short term idea to materialise time lost letting NPC move in the background

While I am less happy with the downtime phase, it’s a key part of the game, depending on your game style it may evolve to the main game, but I use it as a fancy purchase/XP/Heal phase

Urban Thieve campaign

Remember, as the player are stuck in the city, their action matter, treat it like a political game, they’ll quickly need to find allies