If you're a big fan of Critical Role or whatever ever dozens and dozens of live streams or podcasts that have cropped up, you should have enough feel for the game to buy the Player's Handbook and run a one-shot with some friends. Even better if they haven't played before. It's always easier to
start a new group than it is to track down a DM and other people you haven't met before if you don't already know people who are into it.
A couple of other things I think are important to understand also:
- One-shots can be fun but there is nothing like playing a longer campaign, largely because half the enjoyment is from investing in your character and watching them grow -- neither of which you can get from a one-off session where the characters are thrown away afterward. On the same note, scheduling time for a bunch of people to be in the same place for a good amount of their day on a routine basis is extremely difficult so starting one to begin with is very hard.
- You can avoid a lot of drama by discussing with the group beforehand about the expectations of the game. For example, it's best to tell them to try not to metagame too much and do their best to make all discussions in-character. I also think it's important to remind them that the character is their avatar and that they are not their character which is hard for new players to understand. The player themselves might "know" or figure out something but that doesn't necessarily mean their character does, especially in the context of game mechanics.
I've had situations where people read ahead of the campaign book and knew everything that was coming, had arguments about how such and such attack wouldn't work because the range didn't fit the Pythagorean Theorem, debates about whether or not saving an NPC in a certain way was a Women's Rights issue, etc. If house rules were set and enforced as in my second point, all of this could be avoided. As a DM you need to be savvy enough to manage your players appropriately and sometimes even navigate their characters for them (as appropriately justified by whatever dice roll check/save/etc you make them do).