Writing Characters?

[Croik]

I'm going to go against the grain a little and say that if you're having this much trouble with characters, it's because your plot isn't strong enough.

I'm a very plot-oriented writer. If I create a new character, it's only because I have a role I need them to fill. Even at the very start of a project, I'll decide what kind of story I want to tell first, and then decide from there what kind of character is needed for that story to happen. If you want to tell a story about characters fighting, you'll need to give them opposing goals and viewpoints. If they're going to fall in love, they need to have some things in common, some that get in the way. Only once you've determined their worth to the story can you flesh them out with more auxiliary traits. (IMO)

If you're writing your story and two characters are sounding too similar, it may be a sign that the second character isn't even necessary at all and should be cut. Ask yourself why that character HAS to exist. That might help lead you toward the characteristics that make them necessary.

[Zhengo]

Start with something simple, ask some questions to yourself and try to answer them with each character. I'd suggest doing questions that focus on the character's motivations.

What is the thing that the character values the most? What goal is the character trying to achieve, if any? How does this character want to live their life?

Also maybe some simpler questions like what would the character's daily life routines be, what would they do if they were in a certain situation, etc.

Use those answers as a foundation to build the character's personalities, actions, dialogue.

[charliesackett]

You really have to sit and work on empathy to get different kinds of characters going. I think it starts with people watching. As an exercise, pick a random person on a bus or something. Study them. Imagine you are them. What are you thinking? What was your morning like? Where are you going?
Go waaaaay out of your way and pick people as different from you and your experience of the world as you can.

If you don't take buses often, pick a random extra on a show. Pick characters. Pick celebrities. Just whoever until you have a wide database to draw off of for your characters.

[joannekwan]

On a side note: I think people watching is also very important in order to fill up backgrounds and crowd scenes.
All too often I've seen background people share the same style as the main characters in dress, age, and physical appearance.

[SleepingPoppy]

Alright. Then I'm a hermit.

Enjoy living alone in the mountains then?

¯_(ツ)_/¯

[Pan]

In my experience, the key to creating distinct, different characters is their motivation.

Consider your plot. What drives your characters? Is it love, revenge, family, fame, the fear of being alone? Once you have a motivation, it's really a matter of finding traits that can complement each other, but that are not necessarily the same!

For example, I have a personal project I'm working where two character's motivations are the same. They both want to protect a secret. However, one is quiet, thoughtful, but concerned mostly with himself and his family. The other is loud, rude, but ultimately distances himself from those he cares about because he thinks he, himself, is responsible for their problems.

It's the difference between having layers; the first man is selfish, but appears otherwise. The second is abrasive, but actually cares a great deal.

If you find your characters would respond verbally to similar situations, I'd urge you to recall their motivations and write down a Q&A for them, essentially. Answer the questions as that character, note the moments they're too similar or static, and make them more distinct voices.

Or, people watch!

It's great fun, and it gives a huge number of different personalities for your writing arsenal. No conversation required!

Good luck!

[inkythoughts]

I had pretty much the same issue, and what helped me most was writing fanfiction!
And I mean that very unironically.

Especially if you massively struggle with it right now, it's mostly easier to start with fanfiction than original characters. You don't need to worry about "coming up" with different/diverse characters, you already have a cast you can use with preset character traits, backgrounds, personalities, speaking patterns etc. It really helped me to detatch the characters from myself and how I would act on things to more think about "how would character XY handle this situation?"
It also makes it easier to check whether you're still in-character. Just pick your favourite show and write how character X and character Y need to go grocery shopping. Simple things like this, where you put yourself in their shoes and not the other way around.
You will spot certain characteristics that reoccur but that's okay, it's just practice (and a fun one, might I add)! Reading fanfics also might help to understand how other people perceive the very same characters and helps to reflect on your own portrayal, too.

This, obviously, is just for practicing and getting a feel for different characters. You also should maybe switch the POV between several characters every now and then to find their individual voices. And then, yeah, have fun with your own characters! There the others already gave plenty of advice.

(Also don't use the "I'm an introvert" excuse because it isn't - there are so many series, books, movies, etc. where you can start from! You only limit yourself in saying that.)