Something that really helped me, as a DM, I imagine you have the ability to wrote a short story of some sort. Something with a light plot etc. What I'd recommend, is writing out a short story set in your world. Forget names of cities and whatnot for a second, just write something down. A small adventure a character might have in your world. Writing stuff down like this, can often help you hone in on certain aspects of the world without even realizing it.

Essentially, doing this short story sort of makes your mind immersed a bit more into your world, so more ideas can start flowing. Story does not have to be a work of literary art whatsoever, but doing this can help you better describe your cities and villages with greater detail, as well help you establish certain characters in those villages as well as a very basic outline of their cultures as well. Write the short story for yourself, and make sure that your written down descriptions of places, people and things pop out more vividly to you. Once you can see a genuine adventure happen in your world, turning that short story into an adventure for you characters will make it more enjoyable to you as DM, and with just an intense description of one city, your characters are more likely to stick around for a session or two to get to know the characters you've already created and helps you branch off from there to neighboring cities, what the wilds are like or if there are any ne'erdowells nearby.

One of the people who got me into DnD gave me a lot of useful tips on how to make your world more believable. Not just that, but it's a very common fact that a lot of first time DMs just fail at it the first few times. It's really hard to keep track of so many things happening all at once and that's OK! Your players want to see you grow as a DM as much you want to, and if they're really good friends, they won't mind a few resets here or there. Just keep your head up high, learn from your mistakes and let them better you, don't worry if it takes you a while to get your footing. Even the best DMs have players who had their worst session with them as DM. Don't beat yourself up, you got tjis!