Chuck Wendig at his blog says:
. . . the first chapter serves as an emblem of the whole. It’s got to have a bit of everything. It needs to be representative of the story you’re telling — other chapters deeper in the fat layers and muscle tissue of the story may stray from this, but the first chapter can’t. It’s got to have all the key stuff: the main character, the motive, the conflict, the mood, the theme, the setting, the timeframe, mystery, movement, dialogue, pie. That’s why it’s so important — and so difficult — to get right. Because the first chapter, like the last chapter, must have it all.
I read the above just after writing this myself:
The best opening gives you an immediate and normal-life-of-your-protagonist goal that showcases the active agency of the protagonist, something of their character, something interesting (hopefully) about their normal life (eg the minor incident is harnessing a dragon). . . while simultaneously being so simple that no exposition is needed to follow what is happening. Oh, and something goes wrong in the minor incident that will lead you into the major goal of the book.
This is, of course, why novelists go mad.