No backstory. Leave it for later in the book, and even then, keep it brief. Allude to it, make it part of the natural conversation, but never an info dump (my crit partners love that term!)
Give your reader a feel for the tone of the book. Whatever happens in the first pages should set the scene, so to speak, for the entire book. It should act as the jumping-off point, and the readers should get the sense of what the story will be about. It's a promise of what's to come, and you should hold true to that promise.
Make your character someone readers care about. Even a kickass heroine has a soft spot. Show it. Illustrate whatever her particular strength is, and don't be afraid to let readers know she also has flaws and weaknesses.
Most important, write the story you'd want to read. If it doesn't grab you, how will it grab your readers?
What tips do you have for hooking readers in the first few pages?