The arc of each character’s development in your novel can be divided into four sections: Intros, Growth, Climax and Dismissal. This holds true not only for their roles but for the relationships among them as well.
Introductions are usually completed by the end of act one, growth is the focus of act two, rising tension toward a climax is developed in act three, and dismissals are addressed in the denouement or wrap-up, though could occur at any time if a character dies, leaves, or is replaced by another doing the same job.
In the Exposition section, you have already determined something of the manner in which you will reveal your characters' roles and relationships. Now you must figure out specifically in what order to reveal this information about your characters so they are established as real people.
You might tell your readers all there is to know about a particular character right up front. But for another character, you may drop little bits of information over the whole course of the story keeping them mysterious and adding to the intrigue. And, of course, you want to note how a character's outlook and feelings change as the story unfolds.
Then there is the question of who shows up first? Joe, Tom, Sally, or the Monster? Perhaps you wish to first introduce a supporting character and follow him or her until they latch up with a major character. Or, you might reveal several characters together in a group activity.
Who is your Main Character? Do you want to involve your audience immediately by bringing that character in first, or would you rather have them look more objectively at the characters and plot, introducing the Main Character later?
As has already been said, you know all about your characters while your audience knows nothing. It's okay to reveal more about your characters later in the story, but you must lay the groundwork and reveal personality so that your readers can sympathize with their situation and feel for them as the story progresses. For complex characters, it may take the entire story before all their subtleties are revealed.
Sometimes an author may want to have a character with a dark side, or a hidden side that will be revealed only later in the story. Don't avoid introducing such a character, but rather try to introduce its facade as a complete character, making it that much more shocking when they reveal their other face.
Remember, first impressions are lasting, and an audience with the first impression of someone as a good guy, will resist thinking of them as a bad guy for as long as possible. So, don't give hints to the truth right off the bat.
For this step, refer to the exposition material you developed for your characters and then describe how each of your characters is introduced to your readers as a person for the very first time in act one of your novel.