I recommend skim reading any purchased modules to know what to expect before you run them. You'll quickly find your flow of how much prep you want/need for each session. When it comes to running the actual sessions, I try to keep 2 main points in mind every game regardless of game type:

1- Be descriptive. You are the eyes, ears, noses, and any other sensory organs of your players. And to some extent, their knowledge and intuition as well. They only know as much about interacting with the world as you tell them. Help them experience it. It doesn't have to be perfect or cinematic or flowery language. Just get the broad stroke ideas across to them however you can and their own imaginations will fill in the gaps. Practice describing multiple aspects of a scene or NPC/monster. What do they see, what do they hear, what do they feel, what is the mood, etc.

2- Default to saying "yes" in game. I don't mean let them run all over the plot or rules, but if they have an idea, do your best to roll with it. If there's something they want to do, if its remotely plausible then find ways to facilitate it. Even if it's not explicitly laid out in your story or within the rules (or even 100% legal as written). This takes getting used to and often involves going off script and ad hoc rule adjudications. That doesn't mean their idea will always work or that it should be easy, but give them the opportunity to try. The game is collaborative story telling. Players being creative in game can take some of the workload off of you, and make them feel more involved in the story. That means more fun for everyone.