Authors sometimes develop tunnel vision. To take a shot at an easy target (sigh) one of my critique partners asked me straight up, "What's the relationship between the main character and her mother supposed to be?" What kind of question is that? To me it was beyond obvious how the mother felt about the daughter and how the daughter felt about the mother. To me. It's not properly evoked in the manuscript, and so to everyone else, it was an unsettling bit of vagueness, and my critique partner is correct. It needs to be remedied (do you love my use of the passive voice there? Can you tell I'm reluctant to go back and edit?)
I couldn't see it myself because I knew what I meant. I suspect it's the same for the writer I'm critiquing now, and in case it's the same for you, here are some questions to ask yourself.
Is the main conflict of the story reflected in the first thirty pages? I'm not talking about jumping right in with all the juicy stuff you're rightly holding back until the proper time to reveal, but your actual story question. Let's go back to Star Wars (the first film) where our introduction to Luke shows us someone who feels oppressed by his circumstances, feels restless, feels he could do better, and is being held back by the constraints of the man serving as his father figure. We've already seen the Empire in action. Even without Lucas stopping the film to say "Wouldn't it be great if this restless, ambitious spirit could be put to use helping the Rebellion?" we feel that's the direction the story has to take.
Imagine if you just started with Luke going to town with his friends and drinking a beer, getting into a bar fight, tossing a quarter to an intergallactic beggar, repairing a broken droid he finds by the side of the road, chatting with a space trader... All the while he could be dropping hints that he's restless and his uncle is holding him back, and maybe we'd know there are Stormtroopers around. It could be exciting and well-written, but without the larger context of why any of this matters, we won't have a sense of where Luke is headed, and therefore where the story is headed.
You may think it's obvious what shape the story is going to take, or that your characters are pawns of the oppressive Evil Empire, or that your main character needs to develop self-confidence, but make sure it actually is. Go back into the text and actually highlight for yourself that the clues are there.
You have to telegraph the main conflict of the story in your opening. Keep it understated, but include it. Your young magician is going to need to overcome his past? Fine. In the opening chapters, show a way in which that unspecified past is holding him back.
Let's say you're reading a novel that opens with a mom and her seven-year-old child over dinner. There's no father or husband at dinner, and this appears to be their norm. Okay. Well, you can look at the cover or the category and figure out it's a romance, so probably the woman is going to meet someone and fall in love. But you're a bit directionless unless something happens during the dinner to tell us what is the obstacle to meeting someone and falling in love.
Child: "Oh, I forgot. We had a substitute for the afternoon. Mr. Miller got called out all of a sudden."
Mom: "Yeah. Probably fooling around with the school secretary."
Mom: "Nothing. Did you like the sub?"
Gee, she's bitter. Is that her past speaking? Was it the child's father who cheated, maybe her own father? Also, she doesn't mind talking right over her child's level of understanding -- was she treated with lack of respect as a child? Or is she just starved for adult conversation?
These are the tidbits we need in order to form a coherent world view within the story. We're also going to need to know how this woman fits into her society, how her situation compares to those around her, how being single impacts her life and her child's life. Maybe it's beneficial to her to remain single because she's getting a barrel of money every month in alimony -- but show all this. Let us know what's holding her back and what's propelling her forward.
In Save The Cat! The Last Book on Screenwriting You'll Ever Need, Blake Snyder goes one further, and suggests you state the story's theme in the opening scene. We need a signpost so we know where we're headed. And yes, this works with my general aversion to opening a story with an explosion of action. We need to care, and before we can care, we need to know why we care.
If you're on the road and you pass a sign that says Boston - 60 you have your direction, your time, your expectations. It does the same to telegraph the protagonist's hidden need and give a hint at the general problems of the world he's in. Once we know where your story is taking us, we're happy to come along for the ride.