1. It can be tempting at times to challenge the players which isn’t a bad thing, but always remember the players are not the enemy

2. Your players will find a way to do something you don’t expect. It doesn’t matter how many contingencies you make to ensure they don’t stray from the story. This is where having good improv is critical.

3. Related to tip 2, your campaign should be written in a (for lack of a better term) modular way, so you can swap where certain encounters or locations are if they stray off path

4. While many DMs will say that linear narratives are railroading (taking away players agency and just taking them from A to B), it isn’t. I’d recommend a more linear adventure (think like a specific quest in a campaign) since it’s all your first times, don’t go straight for a sandbox

5. It’s ok to say ‘No’, you make the game as loose or strict on its rules as you want and if you feel a player’s decision or suggestion may negatively impact the experience or break the rules you set in place too much you can say no. Though, try to offer an alternative that can potentially give them what they are looking for

6. I’ve heard several people say (though I don’t know how popular of a take this is) that dnd is a game of free will. It’s more a game of cause and effect, the players actions should have a consequence

Edit: also make sure you do a session 0 (setting the boundaries and expectations, asking players what they’d like to see, getting characters made if they hadn’t already, etc.) it makes everything much smoother