Running a game for a new player

I want to make my friends first game really good cuz then he can join our group if he likes the game.

So far I’m doing a coastal murder mystery, a sahuagin priestess is disguised as a town crier and everyday yells there’s been a murder behind the sea wall (behind is the logging area of town and the newer fishing settlement is built beyond the wall). The sahuagin is preparing the town for a raid by makin people move into the fishing area to get shelter from the evil nature spirits of the forest. She kills and drags bodies through the town at night and hangs them on trees and stuff to make the people fearful.

So they’ve gotta figure it out it’s the town crier doing this and not nature spirits to stop the raid before it happens.

Thought it was a good starting adventure as there’s social, investigate and some fighting of course. Any tips on making the game good for a newbie.

Lvl 1 of course.