When you are creating the backstory for your characters, the most important aspect to consider is the psychology of your characters. How do they process information in their minds, and how does this mindset transpire in the actions they take? Once you have this down on paper, then you will know exactly how your character will respond to most given situations or other characters and therefore your novel will be far easier to write. However, this takes a lot of work in the planning stage. So here are a few steps you can take to help you with this. 

Everyone is born with a blank slate psychologically, and as a person goes through life, they meet certain people and go through certain experiences. This shapes their views on themselves, the world and others. Their brain becomes programmed by their belief system. The main reference point for a child is their parents, and this is key to how they will judge certain situations in their future. If a person experiences pain, trauma or rejection, then they will refer to their childhood memory, and from this decide how to respond. If a character had a traumatic childhood, there maybe be a yearning to gain acceptance and love. They may be conditioned to believe pain and love are the same. They may also find it impossible to trust or show affection. Our past experiences may also have contributed to a certain phobia. I know this is true for myself, as my mother had a dreadful phobia of birds which I inherited. As a writer, it is your job to use one of these destructive beliefs as an obstacle for your character to overcome and develop into a more grounded character. 

Most of what pushes a character to behave in a certain way or to have a certain belief system is buried deep in their subconscious.  A character may suppress a lot of painful memories as a way to cope, but the belief will remain as a weight of negativity around their neck. This negativity could be manifested in a way a character reacts to people or situations. There will be a constant inner battle between what they want and what they do. It will show itself in impulse behaviour and reactions. For example, bursts of violence on hearing bad news.  

If you really want to dig deep into your character's personality, then explore whether they are introverts or extroverts. Introverts focus on themselves, their need for self-improvement and discovery of their true calling. Extroverts love being the centre of attention and crave attention and popularity. An interesting concept though would be to create a character that would appear to be an extrovert but actually be the opposite? This would make an excellent character and quite complex, as they could appear to be happy to be single, but actually crave love but have trust issues.

You can break personality types down even further - sensation, thinking, feeling and intuition. Sensation personality types live for the moment, they can be impulsive and creative. Intuitive types are also creative but normally are writers, artists and entrepreneurs. They are huge dreamers and are very focused on their futures. Thinking personalities use logic to solve problems. They use facts, and not gut instinct to make decisions. Detectives are normally this personality type. Feeling types wear their hearts on their sleeves and can be very emotional. They are good at building great personal relationships and make excellent teachers or any career in the caring profession. A person can have any number of these personality types; one will be dominant and the other subconscious.  

Remember strange behaviour and reactions from your characters make for the most intriguing. Let your imagination go wild and create the most amazing people for your novel.