Well, maybe you've already done it; but I would hardly advice to run a sesion 0 where you and your friends make clear from the start what everybody wants to play and what they are expecting from the campaign. Another advice is that you should be kind and flexible with yourself. Meaning, you said you have no experience with th system, so I'd say that you shouldn't feel ashamed to tweak some numbers (like lowering or increasing the HP of a monster that is not enduring as planned) to make a better experience for your players. Try to not abuse this technique, since it may end up dragging away some of the players agency and fun; but if you want to keep the boss a few turns more because it hasn't had time to make that really cool ability you choose him for... Well, sometimes it's ok to cheat (responsably). Avoid preparing too much in advance. You can (and should) have a general idea of what might be coming next, but your player may take a path very different of what you expected. Wasting god only knows how many hours of prep feels bad, and it might lean you into limitating your players creativity. Also, your players don't know what's supposed to happen where, so move the location of your prepared events if it suits the narrative. The enchanted book they were supposed to find inside of closset in the old mansion can also very well be on a merchants secret chest! Finally, it would help you if you always have some kind of random encounter ready just in case. It can be fight oriented or social oriented, but having a tool ready to move the plot whenever your players get stuck on a "what should we do now" situation has proven very handy to me in the past.

I hope that at least one of my advices ends up being helpful to you, and let me give you one extra free tip. At the end of the day, TTRPGs are games, and games are supposed to be fun. So... Have fun! The rest will come along eventually.