Technically, all writing is exposition. Writing is simply explaining, describing, or commenting, which is what exposition is. But when we're talking about fiction, exposition is generally used to describe the act of giving the reader the information he or she needs to understand the story. A certain amount of exposition is necessary if you are to avoid confusing your readers, so exposition is a good thing. But filling your entire opening chapter with page after page of exposition is never a good idea.
On stage and screen, you are limited by what you see, but writing is more subtle. This subtly does not easily allow for the sudden dumping of exposition, especially at the beginning of a novel. If you're trying to squeeze in your exposition, your readers will know it. It will appear unnatural and forced. If a character doesn't have reason to think or say a thing, it will stick out and surely break the spell you're trying to weave for your readers.
Fortunately, getting exposition right isn't too difficult if you're writing in third or first person. It should be a relatively simple matter to include relevant facts when they become relevant. If there is a reason for the character to think or say the exposition, then it fits into the story without being noticed.
The problem writers often run into, however, is assuming the reader needs or wants more information than is currently relevant to the story. Don't include a piece of information in Chapter 2 if it's not needed until Chapter 52. Remember that most readers are just like you and I. They are forgetful. They don't always want to flip back and forth. Unless you have a compelling reason to provide a bit of information well before it's needed, don't do it. One of the exceptions to this is a mystery novel. Mystery readers are quite accustomed to a piece of seemingly irrelevant information coming back to haunt your characters.
But in general, you should not force a piece of information before it is naturally revealed by the story. If you are dumping exposition upon your readers, make sure it is invisible. Have a character who is excited or frightened reveal too much. Make sure your characters have a good motivation for thinking or talking about the information you are presenting. And don't do it in your opening chapter. Your opening chapter is for hooking your readers, not confusing them with bits of information they won't need until the end of the story.
For exposition to be seamless, it must be motivated by the facts of the story. There is an element of timing involved, and one of relevancy. Just because you, as the author, feel the information is important doesn't mean it should be presented right at that moment. There must be a reason, or it will feel chunky and out of place.
The best story beginnings aren't filled with a bunch of facts that don't make any sense yet. They are filled with brilliant descriptions, vibrant characters, and unanswered questions. Propel your readers into your story before you start dumping exposition on them. Even if it's necessary exposition.
