Awesome that you’re taking on the great honor of sitting in the DM’s chair hahah xD. I’m still a baby DM myself, running a campaign since April. So while I don’t have the wisdom of a veteran DM like some folks here, I can offer my two cents as a fellow newbie (who has a PhD in watching DnD YouTube videos, if that counts for something). 
Okay, so: It absolutely helps to play a few sessions at VALUE. We have so many great DMs here <3 Through VALUE, I got to experience different DMing styles from different people, which helped me figure out what I like, what works really well, and what I want to adapt for my own games. It also gives you a sense of how pacing works and what to do when things slow down, or how/when to nudge your players along so the game doesn’t bog down.
Pacing (!!) is sooo important, and honestly, books or YouTube videos don’t really teach you that?? I think??? You need to experience it 
When it comes to storytelling, there are a million great YouTube videos, but one I found particularly helpful is the 3-act method:
What also helped me is taking inspiration from popular media tropes and arcs. Think Lord of the Rings, Marvel’s Infinity Stones storyline, etc. Some might say that’s “”“UnOrIginaL”“”" but clichés are clichés for a reason. Especially as a beginner, sticking to the basics is a good thing! You can always add layers to the story as you go. That’s how I do it at least, espcially by bouncing off my players’ ideas.
Yes. Bounce off your players’ ideas! Listen to what they’re saying. You can usually tell where they want to go next or what they’re interested in. Aaaand bonus point, build the story with their backstories in mind! No matter how epic your story is, what they’ll actually remember are their special moments. <3 Give them their special moments.
A formular that I’ve found also works very well: Motivation + time-crunch. Having goal, even if it’s vague, mysterious, or just a short-term objective PLUS a time limit of some sorts is usually a great way to keep players moving and prevents them from wandering aimlessly.
Lastly, world-building. I don’t really do it, so I can’t say much there ^^’ I use Faerûn as a baseline, but I’ve told my players this is my version of Faerûn, so some things may be different. Maybe that’s something you could try? Or only focus on certain areas first. A friend of mine hosted a one-shot and only had one area built and planned on fleshing the rest out as the story went on.
As the others already said, having a perfectly fleshed out world isn’t necessary to start playing. In my opinion, having a fleshed out world & GoT-level plot isn’t important at all (hot-take). More important is that it feels ALIVE and you give your players stuff to do and find.
On that note, having various encounters and activities ready to pop in as “modules” is super handy! For example, I might have one or two soft-built locations I can throw their way if they need somewhere to go. Or I’ll prep stat blocks for bandits or monsters I think they might run into. Just in case. This comes in especially handy when I’m underpepped xD
Sorry for that rambly wall of text, I hope it helped haha xD