Top piece of advice I can give to a first time GM is grab a game and run it. A few one shots or short adventures will let you get to grips with being a GM/storyteller independent of a specific system, so you can work out what you do well before starting a full campaign. Beyond that:

• Don’t over-plan. Even when everything goes to plan your players will somehow surprise you, so keep your plans broad enough that you can herd them towards specific goals and events without relying on them taking specific actions to get there. Be prepared to rearrange events and improvise to keep things on track.
• “Yes, and” is good, but “No” is a complete answer. Just because a player has an idea doesn’t mean you have to go along with it, and if someone’s trying to ignore the story you can just say that their character goes on their own adventure, make a new one. You should accomodate players where you can, bend the rules here and there to make things more fun, invent locations and improvise NPCs in response to their attempts to interact with the world, but don’t let them dictate the adventure to you.
• Communication is everything - tell your players as much as you can, before, during, and after sessions. Tell them about the setting, the locations, and the NPCs they’ll already know when the campaign starts. Feed them extra tidbits of information that don’t come up in game but help flesh out the world. Talk to them about their characters and their feelings about events or NPCs, and talk to them about their own feelings on the game, what they like, what they dislike, what could change or improve. They will engage with the game a lot more if they have stuff to engage with, rather than turning up to sessions with a random character to glean what information they can from your descriptions.
• Description is also everything - your words are the only conduit the players have to the world, so try to use all 5 senses to immerse them. For everything you describe, start with a few adjectives (e.g “a small, dark, square room”) and then add details (“with walls covered in grey lichen and a strong musty smell”) before moving to the next thing. For creatures, describe things like posture and clothing. If you want a better descriptive vocabulary read short stories - they tend to be 2 paragraphs of plot wrapped in every adjective in the english language.
• If you want to play D&D don’t actually play D&D 5e. It’s unusually unfriendly to any GM, but especially to new ones, because its surface simplicity comes from there not really being anything underneath - you are expected as a DM to just know how to create and adjudicate mechanics on the fly, and the rules only cover a fairly barebones fantasy, relying on homebrew for a lot of things. Also they keep adding problematic elements to the game - only two years ago they managed to change spacefaring monkey-like people into deeply bigoted caricatures of african americans. You just don’t need that shit. If you want the same fantasy experience play Shadow of the Demon Lord/Weird Wizard or Pathfinder Second Edition. Shadow has the straight forward simplicity that allows for spur of the moment rulings that 5e thinks it has, and is easy to pick up or improvise with, while PF2e is closer to 5e’s actual complexity, but with tactical combat and a mechanical unity that makes it more intuitive to play and GM. Pathfinder 2e in particular is “D&D without the baggage”, with really interesting and inventive lore and adventure paths, and an emphasis on inclusion, working with ethnic game designers to include their cultures.
• Lastly, the primary objective is to have fun. If a part of the game is getting in the way of anyone’s fun, change or get rid of it. If the rules regularly aren’t working for the group, grab some different ones. Sometimes there’s a bit of a hump to get over while you get used to a system, but don’t bash your head against part of the game to keep it moving - You are only doing this for fun, so if it’s not fun don’t force it.