Sidekick, supporting character, minor character, "the friend".... they're all accessory characters. Some may be more important to the story than others, and their development will vary. However, just because they aren't the OG or Michael, doesn't mean that they can easily be glossed over. From being a sounding board, to the superego, to the troublemaker, to the nosy neighbor, to a person walking down the street, supporting characters have the potential to add bring life to your main characters and the plot. They can also be hindrances, if too shallow, unbelievable, overly detailed, or numerous. Having written on the OG/Canon lead, this segment will detail ways to make sure that your cast of supporting characters (large and small) is conducive to the needs and goals of your main characters and plot.
Adding Authenticity to your Fiction.
One common misstep is thinking that all or most of the minor characters need to have names and backstories. To be honest, that's not true. Think about the situations in which you come into contact with people who you know nothing/next to nothing about: at the grocery store, in the Ladies room, at the mall, walking across campus, walking through another department at work, etc. Yes, Michael led a life that was often plentiful in employees, but still. I doubt he knew a ton about each employee or shared his innermost feelings with each backup dancer. As such, having some characters that are just there to fulfill a role (e.g. waitress, cashier, fan, pedestrian, bartender, assistant to a manager, etc) is fine. Sidewalks have people, streets have cars, stores have shoppers, and Michael had fans that followed him around on a daily basis.
With regard to these individuals, don't get carried away with description. Some may have names, some may not; some may need a two sentence introduction while some only need one. Organize these details into shorthand that also conveys a note on the context. For instance:
Hearing the nearing sound of wheels on uneven sidewalk, she quickly leaned against the chain-link fence. A second later the skateboarder sagging and a black baseball hat zoomed by.
Note that I only described an action, with three things - a skateboarder, a chain-link fence, and a sidewalk. However, I bet most people found that their minds filled in the blanks. Having these walk-ons means adding people to your story without making them all major characters or developed supporting characters. Without them your characters are trapped in a bubble.
This may look like fun, but it's also undeniably awkward
Introducing your Minor and Supporting Characters.
When introducing minor characters, do so with care. By that I mean, have them make an impression, but don't make them the center of attention. After all, they are "minor", right? For instance, if introducing a best friend do it in the context of the person doing something a best friend would do. Give the person a bit of dialogue and an action, but don't get sucked into the trap of telling a long backstory of how they met or inch-by-inch details of their body. If the backstory is important, weave it into the story gradually or have a character reflect upon it when the time is right. Remember that with supporting characters, the focus is on them, but in how they play off the protagonist and further the plot.
Of note: thus far I have used the term ‘minor' and ‘supporting' interchangeably. Some ‘minor' characters might actually not be so minor. These would be considered more as ‘supporting' characters. While these supporting characters may be more visible and developed in your story, make no mistake: the sole purpose of a supporting character is to interact with and/or otherwise engage with the main character(s). They can have more developed personalities than a minor character, but they are still there to support the main characters (note: I use this term interchangeably with the terms OG and Michael. In the context of MJ ff, they're generally one and the same). These supporting characters exist, make statements, and take actions that are intended to affect the OG and/or Michael in a way that will give us a better understanding of that main character.
My Name is....
Please, please, please, do not give characters very similar names. When that happens, it becomes easy to confuse them, and the reader will often become annoyed by the fact that they can't keep the characters straight. Think about the character's personality before you name them. This could result in the character having a nickname based on their personality, surname, first name, heritage, etc. Remember that the more characters there are, the harder it is for the reader to keep their names straight. As such, please do not alternate between nicknames for the same person. Also, vary the name lengths. It's harder to confuse a Jose with a Ricardo than it is to mistake a Jessica for a Monica. Pick names that vary in length, first letter, and sound. Finally, we don't need to know everyone's middle name. Remember that including that can be too much, as it is one more name for your reader to remember.
Developing your Supporting Cast.
While I don't recommend putting a character's full history when introducing them, it is important to add depth and baggage to the more present supporting characters. Just as when choosing character traits one needs to be mindful of the OG and MJ's character traits, the same is true in fleshing out a supporting character's baggage. Remember that each element comes with consequences. For instance, if a character has kids, those kids can't suddenly disappear or be without care. Ditto for pets, spouses, family members, etc. It might help to start them out as a stereotype, but then develop them alongside your main characters, so that they can better play off each other and add depth to your main characters.
The thing is, if you do decide to develop and include a supporting character, be careful that it doesn't overpower the OG or Michael and that you pick and choose which supporting character gets this extra time. If you make the fatal mistake of developing too many supporting characters, your readers will be left trying to remember names, histories, and get bored when the story deviates from the reason they began reading: the OG and Michael.
Balancing your Characters' Traits
Every story needs this, whether it is a fanfic or a classic novel. If Michael is naïve, then having an assistant that is wary, can work to balance him out. If Michael is arrogant and has a tendency to get wrapped up in himself and his problems, a manager or bodyguard that will challenge him and make attempts to distract him from himself, will lessen these traits. These opposing character traits rely on the basic cliché that opposites attract. So why does this cliché work so well, when others can fail? Because, including opposing character traits can create realistic chemistry and further character development. When characters are constantly in agreement, things get boring and no one really needs to change. Moreover, having a supporting character that contrasts with a main character can intensify some of the main character's traits without the author having to appear as though they are constantly complimenting him/her. For instance, it's unlikely people would read Sherlock Holmes as being so smart, if he didn't have a dim Watson by his side. So, when approaching writing a best friend, an assistant, or some other version of a side kick, begin by thinking about the OG or Michael's personality and what kinds of opposites would best work in your story.
Just as your main character could use someone who balances his/her traits, he/she could use an antagonist. Now, I'm not talking about a villain, just someone who opposes the main character. Essentially, I am talking about an adversary for the main character to knock heads with, to push his/her buttons, and otherwise add conflict to the main character's life.
Adversaries often aren't utter and complete enemies.
This can be accomplished in a number of ways. It could be a manager who likes everyone to be on time and micromanages everything. It could be an overprotective family member. It could be an attorney or police officer that is too stuck in their ways to listen to others or examine different angles. It could be a broke reporter who needs something that can make them money, regardless of whether it is true. There are a number of different approaches that you, as an author, can take, that avoid the classic "this person is evil" cliché. Regardless of how you develop this, keep in mind that this character should have opportunity to get in your main character's way.