Decide the physical appearance:
You must start with the appearance as this will help you in establishing your character without putting any extra effort. Do some research on details like height, overall look, complexion etc. Then add some minor details like tattoos and scars of wounds.
Give your character a Personality:
Next thing you need to do is to give your character a personality. You can do this even without the script as this only shows what kind of person that character is.
Does it fall in the category of emotional characters or cold ones?
Does that character have some passions or just living life?
Deciding your character’s behaviour, mind-set and manners will help you to determine its actions and reactions. Ultimately, a film is all about actions and reactions.
Decide its flaws and qualities:
As the mistakes and heroic deeds move the story forward so you give your characters some flaws and features. This will not only bring your character close to the reality but also help you to develop a powerful story. Mostly, films follow a set pattern in which the main character makes mistakes and then overcomes later on.
Develop a background:
After developing its psyche, you should give your character a background which plays a vital role in everybody’s grooming. Make sure that your character has logic behind its every action. Work on its life story and tell how he became that he is now. Background is always an effective part of script.
Combine the character with plot:
Next thing you will do is to fit the character in the plot. Make sure that it becomes a part of the story as there will be no benefit of developing an irrelevant character.