That sounds like quite a project, but fortunately it’s been tackled by other people out there. The D&D website has an article about running modern games: https://dnd.wizards.com/articles/features/my-new-d20-modern-campaign
I did a google for 5e modern and there’s a lot of articles and blog posts on the subject. Also, you can go to DriveThruRPG and search for free material. They have a lot of Free RPG Day and Quickstart publications from years past.
Also, consider doing a Session Zero with your players to talk about their PCs and your campaign hooks. You’re creating an original setting, so enlist them in finding out what kind of game and PCs they want to play. Their PC ideas can provide you with story hooks that they’ll want to engage with, and they can help guide the contours of the setting.
My bottom line I think is that being a DM is hard work and you should feel good about offloading as much of it as possible. Your players and the army of nerds posting on the internet are two great resources for this.
I am going to be running my first campaign soon. It’s going to be based in the near future, in big cities and stuff like that. Any tips? (I’ve only played a few games of D&D, so you may have to dumb some things down for me.)
What system are you using?
I think my biggest tip is to steal and repurpose anything you can that would make a good adventure. Any D&D or other adventure books you have, movies or novels, pretty much whatever. You can probably reskin it to match your setting and drop it into your campaign.
@thelrik I am going to be using 5e. I am loosely basing it off of Cyberpunk 2077 and other semi-post-apocalyptic video games, along with integrating some Eberron aspects. I reskinned the classes for the campaign too, so Barbarian = Police Force, Artificer = Scientist, etc.
And don’t be afraid to allow the gods to take a roll.
Never EVER did d&d, but was GM/DM/GoD in other systems and one allowed you to worship a set of gods who you could roll for a attribute and had to take it good or bad. Got +2 skin once, LOL. Loved it. Another friend played a semi-sentient manticore, int=3, yes, 3, it was a blast to GM with that as a part of the party!