---In coming up with a story that involves one or more characters--
The first and main principle in writing a character is credibility. This is what one must need to be create a good character.
The reader has to believe this is a person.
It may sometimes help to create a character by drawing from life, as people you know, watched or seen, maybe even a combination.
Believe ability of a character comes from how they act, speak, or react from their surrounding. Even if the character is a wizard, elf or warlord in a fantasy, one must make it believable.
No matter what, a character has to be human like. Take for instance Spongebob Square Pants from Bikini Bottom. He is not technically human, he is part of the human condition, he is never the less essentially human.
As the Wizard, elf, war lord, and Spongebob they all have desires, fears. sadness, jeaulousy, happiness, goals, and accomplishments, which makes them like humans even though they are not humans.
An important aspect of character is they have to have purpose( something to do) as a main character.
One fact about all readers is we don't want to read about heaven as much as want to read about hell.
I've approached a character at one point and gave him a setup of a normal life and asked myself how can I ruin things for him, how can I make him miserable.
We want to see characters faced with dilemmas to see them suffer, we want them to have problems to overcome. Adding stress to a character and writing how they deal with this stress will show the reader the real character.
Actions speak louder than words, this may be a cliche, but it is true none the less.
One of the most difficult things about writing fiction is allowing the characters actions to speak for the character rather the narrators exposition.
Watch how the two following examples follow a character and develop the same character.
exposition: Rob was an alcoholic
action: Rob staggered through the kitchen flinging open cabinets and then slamming them. He checked the fridge - nothing. He rooted through the empty glass bottles, staggering through the apartment, praying for a forgotten drop of fire water. All were empty. He took the garbage can, which was stuffed far above the brim, and he dumped it on to the kitchen floor. Down on all four knees routing through the waste he snatched up a fifth of Taaka Vodka that still had a few remaining shots left. He gripped the slimy bottle and upped the bottom and drank lavishly as he held it over his opened mouth until the very last drop fell.
The two examples above show the difference between telling the reader and showing the reader.
The action and scene shows the reader that Rob the alcoholic is Rob the alcoholic. The writer shows the characters behavior, and the reader should be able to make their own judgment.
That is what characters and plots are there for.
Think of any movie you have watched , what do you do?
You judge the character and think about what you would and wouldn't do if you were that character.
A Good exersice would be to go through any writing you have and look for this construction s+be+subject compliment
Jim was angry.
Faith was a slut.
Mark was lost.
This is where complexity of nature comes in. For instance, when I am angry I tend to slam doors and throw things, but when Jim is angry maybe he bites his lips until it bleeds or counts to ten and takes deep breathes or maybe he climbs the clock tower with a rifle and starts sniping kids at the park.
The point is that telling us that someone is angry comes off flat and uninteresting, but to show a character act out of anger will enliven the character for the reader.
I develop a theme and setting to put the perfect character in there. I then make the character come to life and live in this theme and setting. I throw in delima's and solutions, and he struggles until he either gives up or achieves what it is he has set out for.
The greatest definition of a protagonist is a character that has a desire, goal, or objective that the character has to do to achieve them.
A good protagonist is proactive and goal oriented. A compelling character is one that is compelled to move, to act. Something must drive the character forward, and as the character moves forward the plot does as well.