Are you tentative about introducing new characters? Afraid that too much attention in creating newcomers will allow them to overshadow your main characters? A variety of decisions must be made: How fast to introduce characters, how much detail to give, and which techniques work best for seamlessly bringing newcomers into the story without slowing down the action. The answers will depend on point of view and the role this new character will take.
How fast can new characters be introduced? Think about characters in the same manner as digits in a telephone number. A seven digit number is fairly easy to remember. However, within this telephone number, the digits are divided into two groups: three and four. If you have a number of characters that must play a role early in the story (i.e. first and second chapter) it helps if these people are introduced as part of a group. Three to four is a good size.
Trying to bring in more than seven named characters at this point is likely to overwhelm your audience. However, during the remainder of the story, you probably don’t want to introduce any more than seven more named characters of secondary stature (unless your name is J.R.R. Tolkien).
Next, comes the question of appearance: Is age, hair and eye color enough? How about height and weight? Remember, this is a character intro and not a driver’s license. Only enough physical description to distinguish this person from other major characters is needed. That might not be any of the attributes found on a driver’s license. The shape of their eyebrows, the manner of their smile, or ever gait of their walk can be the memorable trait.
If the point of view is first person, and the narrator already knows this person, no physical description may be necessary. The narrator’s relationship to and opinion of the character should take center stage in the introduction. Whatever the point of view, boil down the physical details to the few most important ones. The reader needs to know about characters through their actions, how they relate to others, and through their interior thoughts or other’s opinions.
Most important is how to introduce new characters. Their backstory is of negligible importance. The reaction of the protagonist or another character who encounters this newbie is what inserts them into a story in the way that readers will sit up and notice. Your main character doesn’t need to have a conflict with everyone that crosses their path. But, disagreements need to be more plentiful than in real life.
The new character should arrive with an agenda that puts them at odds with a character that the reader is already invested in. A conflict or misunderstanding with the main character is the strongest way to introduce this person. Even if the two are going to become blood brothers or the devoted lovers later on, the new person should pose a problem which the protagonist needs to overcome. Imagine how short Pride and Prejudice would be if Elizabeth Bennett had not misread the character of Mr. Darcy.