The beginning. It's the door to your novel and you want people to open it and make themselves at home. But how to accomplish this? Do you begin softly? With a big bang? Throw the reader into the room milling with people? I believe, in this case, that not one size fits all.
Thrillers demand you throw your reader straight into the action. Within a few sentences your protagonist is in danger or has danger creeping up behind him. The beginning must be fast-paced and (let's face it) thrilling. Character introductions are minimal, simply because this genre's characters are instantly recognizable. There will always be some form of the brave hero, the faithful sidekick (usually of the opposite sex), and the villain bent on world domination. Bring on the hungry sharks.
There are also the books that begin in the middle; in mysteries this could mean the discovery of a body before the first paragraph is finished. I have found mystery readers wait hungrily for that first body, so I either throw it at them right at the beginning or tell them in no uncertain terms who is not going to be coming to dinner. Once the body (or the hint of one) has been given, many mystery readers will sit back and happily get filled in on the action leading up to that point.
Then there are the soft beginnings in which the reader is gently introduced to the novel's world and the people that inhabit it. These beginnings work nicely in humorous novels; after all, you have to know the world right-side-up before you turn it topsy-turvy.
Another problem: What is considered to be the beginning? Is it the first sentence? The first paragraph? The first chapter? Common sense has taught me if I haven't hooked my reader by the end of the first chapter, I'm sunk. People judge quickly and harshly. Reading a book, after all, is something one does for pleasure. Bad beginnings almost always ensure a book may be started, but never finished.
Pace is also important; a fast-paced beginning can't slide into a meandering trot through the middle. However starting slowly gives an author plenty of opportunity to quicken the pace as the danger or the comic mayhem increases.
How do you approach your beginnings? With a body? Hungry sharks? Everyone sitting down to tea? Or is it with a description of a sunlit meadow and three horses grazing peacefully in the dappled shade of a large elm tree?