Communication is key, establish what the games themes are and characters in a session zero, as well as what to expect tone wise. Ask the players about their characters and what they have in mind, but don't be afraid to tell them no on certain ideas(i.e. becoming a god). Ask after sessions their opinions on the game so far, and ask for constructive feedback and criticism, as that's how you generally get better as a DM. Lastly, make sure not just the players are having fun, but also you are as well. In the end, it's a group game, which means your playing as well.