Be an observer – look at the people around you and study their behaviour. Analyse their actions: what are they doing, why? Is it genuine or are they trying to hide something about themselves? What is their greatest weakness? Their greatest strength?
Spend time with your character – think about them in circumstances other than the scenes in your novel. How do they eat breakfast? How do they take their coffee? What do they do when they are stressed / happy / angry?
Fill in a questionnaire for your character – you can download some great ones from the Internet or else create your own. It should include details about physical appearance but also and perhaps more importantly about them as a person: things like their favourite memory, their greatest fear, their biggest secret, their typical day etc.
Don’t panic if the character doesn’t arrive fully formed. As with all other parts of writing, it’s about layering. Each draft you write should hone not only your plot but also your character as you get to know them better.
Have fun! You’re making a person! Enjoy it. Make your characters vivid and real.

Five tips for creating character was originally published on A. J. Grainger