For making a campaign, you generally want one thing: Someone has to want something. The lich could want the throne, the archwizard could want research material from the astral plane, the PCs could want immortality...
What I'd suggest, make a world first. Some nations, cities, even just some basic ideas on what's in what area of the world. Paint some terrain in broad strokes, and put some sort of people in every region. Then put in something or someone that's upsetting the setting, like a lich who's marching out of the swamps and into the kingdom. Now the party has to defeat the lich, so now you need to decide where the Phylactery is, what legendary sword will cut off his head, what secret mountain cult is hiding the blade...
One of the more solid ideas, I think, is to make a fairly simple goal - The dragon may only be slain if his heart is stabbed by the sacred blade. Then put the goal behind a small number of quest chains, and put all those behind random interference. Like, to get the sacred blade you have to prove to the monks you're ready, and they want you to fetch an amulet. The amulet is on the other side of a goblin village - the goblins aren't worried about the quest at all, they're just goblins doing goblin things. Similarly, the swamp they live in isn't a quest item, it's just a swamp doing swamp things. And the wyverns... Just sprinkle the area in unrelated but similar-CR problems.