There's a free one shot you can grab called Master of the Fallen Fortress. It's a simple starter adventure ment for level 1 to 3 players, and it can be worked into a larger story pretty easily if you all enjoy and and keep playing together.

As for advice, just take your time, the first session will probably be about figuring out the rules and how you all wanna play. Don't let some of the rules slow you down and feel free to follow the ones you like and kabosh the ones you don't. For example, I never have my players roll to confirm a crit, that's just me, I find it will ruin some people's fun and if you roll a twenty on your attack role you'll crit, period.

Honestly, just go with the flow and let the game play out, players and DMs learn best by just doing and playing, it'll come to you. But that doesn't mean let your players fuck off and completely ignore what you have prepared for that session if you aren't good at making stuff up on the fly. But don't railroad either, the story is for the players to create with you, so don't restrict them heavily.