Instead of focusing on imaginary rules, focus instead on an effective way to tell your story. Perhaps it's not usually a good idea to start a story with the main character sleeping, but I'm doing it in my upcoming novel, Angels' Kiss. Why? Because I need to establish that my main character is a novice seer but doesn't know it, and I need to do this quickly. In the world I've created, this particular gift first manifests itself as prophetic dreams before expanding to full visions while the seer is awake. So the quickest and most effective way to convey this information is so start with her asleep and dreaming. It also allows me to foreshadow a great deal of what will happen later in the novel, and it means I can get to the meat of the book with impressive speed. While it may be frowned upon by some, this is best for the story, so the "rules" go out the window.
As for the dreaded impact, making an impression with that terrifying first sentence, well...there is some truth there. You do need to hook your audience fairly quickly. Maybe not in the first sentence, but definitely within the first page. But you don't need to kill anyone, make anything explode, or frighten the wits out of anyone to do it. You just need to start the story in a way that makes people want to keep reading. Ensure the first page makes readers question what's going on, offers some intrigue, or at least is well written enough to prompt most readers to keep reading.
But how do you do this? First, relax a little. The idea that you have to nail your first line is truly a myth. Readers always read past the first line before buying a book. They often read past the first page. Think about how you yourself buy books. You're not an idiot about it. You don't require death and blood and gore on the first page. Neither do your readers. Give them some credit and relax into the story before you start writing. Give the story its due and start in a manner that makes sense for the type of story you're writing.
Don't worry so much about starting with a bang, literally or figuratively. Instead, think about how the reader will orient themselves to the story. When a reader picks up a book for the first time, it's a little like being thrown into the ocean. You don't really know which way is up, and that's not a good feeling. Readers want to feel secure in where they are and what they're doing, so a completely mysterious beginning may make them uncomfortable. Though there are readers who like to be confused, most don't. If you want to appeal to your audience, use your first paragraph--or first page--to help your readers find their way. Answer a few questions. Who is the story about? Where is this person? What are they doing?
In the opening paragraphs of Angels' Kiss, I establish all these things. Sorcha is a young lady in bed, dreaming a fascinating dream. This, of course, poses several other questions, which is what the "hook" actually is. It's not the first words on the page. It's the promise offered by the first words on the page. The questions that arise are what prompt the reader to continue. When you run out of questions to answer, your story is over, so the beginning must absolutely ask and answer at least a few of these. How you do this is really up to you.
The point is this: your readers can be hooked in any number of ways. You don't need to get ridiculous about it, you don't need to be too clever, and you really don't need to stress too much over it. If the first page of your story answers a few questions, and poses a few more, your readers will keep reading. But if you try too hard to intrigue or shock, that alone will turn readers off. Let the story flow naturally, especially at first. If you need to tweak your beginning sequence a little later, you can always do that. It's paper (or a computer screen), not stone.
