Welcome to it! One thing that helped me is knowing what everybody wants out of the game, including myself. If everyone is having fun, that takes a lot of pressure off the DM. Talking to your players about that can be useful. But, a lot of the time, asking what a player thinks is fun gets the same answer: “I like a mix of combat and role-playing.” Sometimes it’s better to just ask what their character’s wants and goals are. Someone that says “my character wants to recover the secrets of her lost memory” will want something different from someone that says “my character wants to become the ultimate killing machine.”
Doing, ahem, homework, also helps. I’ve gotten a lot of use out of reading the Sage Advice Facebook page, too. There are more resources to improve your DMing than every before. When there’s a rules question, don’t be afraid to make a quick ruling, but then tell them you’ll do research and come up with an official ruling next time.