I like the opening line to Neil Gaiman's The Graveyard Book: "There was a hand in the darkness, and it held a knife." It's very dramatic, and from there it continues to build the tension about what happens to the MC's family and how the MC, only an infant, escapes. Interesting enough, we do not learn the identity of the knife holder until the end of the book.
On the other hand this is how Natalie Babbitt opens Tuck Everlasting: "The first week of August hangs at the very top of summer, the top of the live-long year, like the highest seat of a Ferris wheel when it pauses in its turning. The weeks that come before are only a climb from balmy spring, and those that follow a drop to the chill of autumn, but the first week of August is motionless, and hot. It is curiously silent, too, with blank white dawns and glaring noons, and sunsets smeared with too much color."
No characters or plot at all, but it is just as memorable. In both cases, the writing compels us to keep reading (or this reader at least). Same with the opening of Harry Potter, which only hints at things to come and only incidentally mentions the MC. So there are many ways to start your book. If you think it is too flat, is it because it starts in the wrong place, or is it that the writing itself isn't compelling enough? Probably the best way to figure it out it to have another pair of eyes (or better, several eyes) take a look and offer up an opinion. If many are coming to the same conclusion, whatever that might be, then that is something to be considered.
