As a long time writer I can tell you that coming up with a character is one of the most fun things about writing a story. Your possibilities are endless and, after all, what is a story without characters? The plot may capture you in and the universe in which your story is set may be immersive but what good is that if we don't have someone to take the journey with? Characters are critical to a story, therefore it is essential to make sure you have good ones.
One of the hardest things is truly bringing that character to life. Most people realize that their characters are more than just a cool person who their story happens to focus around. You need to see them as if they were a living and breathing person. A character is more than appearance and action. Seeing a character as a person can be difficult, especially if they're outside of what you're used to writing. But, that being said, a character beings before you even begin writing them in.
There are a lot of different places you can start with creating your character. They could be based off how you want them to look, they were brought up by the need to further the plot, they can just be someone you thought of out of nowhere. A character's origin does affect the way you think of them at first so remember that.
Depth is important. Very important. Knowing your character inside and out will help you greatly. From their favorite food to their worst fear and greatest achievements to their overall goals in life. Knowing these things is a way to create a level to them that establishes that they're an actual person.
These things started from when they were kids, all the things they like and want to do. That makes it even more important to really know their backstory. What were they like as kids? How were they raised and what was their home life like? What, as they grew up, shaped them into the person they are now? This is probably one of the most influential things you can know about your character and is definitely one of the most important.
This connects with another important thing; your character's motivation. Why are they doing what they do? What do they hope to achieve? What lead up to this and gave them their motivation? Knowing your character's motivation and convictions make it a lot easier to determine how they act in certain situations and more clearly defines what they're willing to do to achieve their goals.
The next thing I have here is something I struggle with when I'm writing. Giving your characters their own personality is excruciatingly important. Since they're their own individual person they'll speak a certain way, do certain things. Everyone has their own little quirks and habits and it's a good way to make them feel more real.
Understandably we'd like our characters to be strong, valiant and undefeatable. Unfortunately that's not in the makings of a good character. Characters have strengths and weaknesses just like everyone else. They can't be completely impervious to everything. Their weaknesses make them relatable, as do their strengths.
There is a lot more about characters that can be said but it's a process. Writing your character will be easier and your audience will be more invested in them. Happy writing!