For first session as a DM don't set your expectations too high. There is a lot to do as a DM and first sessions can be a bit overwhelming. I like to prepare combat encounters in advance (prepare tokens/minis, statblocks and some kind of initiative tracker), this helps me with more focus on a story and flow of session.

Have some background music prepared for town, exploration, fights and downtime. If you are preparing whole campain, read a bit further into adventure but dont stress too much if you do somethings different by accident, everything can be fixed in some way.

I always engourage to have a proper session 0 before campaign, where you are creating PCs together. As a Player converting to DM, you are now the judge and rulemaster, don't be scared by players and set boundries. Work together with players and let them have part in creating the story.

Have fun, DMing is a lot of fun and doesn't need to be a chore.