I got burnt out making up the world, its mythology, every person in the world, and the adventures.
Yeah, that's a good point. And the lure of that is deceptive -- most DMs
like that kind of stuff, so they don't even realize how unhappy it's making them until they're just burnt out and want to quit.
It really pays to know when you've had too much of a good thing. Know when you're feeling obligated/compelled to spend hours & hours on backstory and fleshing out the world. When you get that feeling, back away and find ways to cut things out or use modules or otherwise aid yourself so that you don't end up overworked.
The other thing is to sit down with your players and figure out what kind of game they want.
Yeah, that's a really good idea, although there is another side worth noting. That is, you need to know what kind of games
you want to run, too. If all your players want combat and you want roleplaying, you need to know that you're going to feel miserable if you run their game. In many cases, there is common ground. However, I know at least one campaign that ended abruptly because of this stuff. So know how to have fun instead of having obligations. The moment D&D is an obligation, game over.
I would add a couple of my own ideas. If you're first starting out, overprepare. Generally, when you're first starting is your highest energy point, and it's also the place where you know the least and are capable the least. So use that enthusiasm to compensate. If you want to read advice, do. If you want to read a module, do. If you want to roll some dice to playtest an idea, do. Induge your enthusiasm, at least at first. Know your game world, know your NPCs, know your plots, and know what to expect from your players (ask). Even with all that, you should expect your first session will throw you for a loop. You'll have a monster that you think will be awesome, but the party will wipe it out in 1 round. You'll have a town for them to explore and they'll ignore it entirely and ask you about the forest which you never researched or planned for. And so on. Expect it.
My other tip builds on that. It's sort of my own personal advice cliche, as I say it every time one of these threads pops up. And that is,
your players don't know what you know, so feel free to move props around. I've seen DMs fall apart because their main bad-guy was killed. Those DMs never realize that often the players don't know they killed the BBEG. And therefore, they have no idea if you just quietly give that NPC a different name and rebuild your BBEG with better stats for the next week. Once you realize things like this, it is so freeing. You realize that your plotline can live on, even if the players just broke something. You realize that all your work in some amazing stat blocks can be salvaged for another quest. And so on.
Once you know that, you'll never be like the DM in the "Wall of Force" thread, who absolutely positively insisted that his dragon sweep down on the players, even if they had a pretty reasonable way to stop the dragon. Instead, you'll be able to roll with the punches. You'll be able to let the players have their moments (which is kinda the point), and then you'll go about changing your game world so that you can try your strategy again with a different monster or something.