There’s no shortcut; if you want your story to engage the reader, then they have to care about the characters, and that means they have to be compelling. So, what are the emotions your characters need to evoke? Well, they need to be believable, relatable and make your reader curious but achieving this is easier said than done. Have you ever created a character backstory that seems to have covered every aspect of their lives, but something seems to be missing, that one secret ingredient that makes them jump off the page? It may have something to do with the one missing piece of the jigsaw. You have failed to give your characters believable fears, struggles or desires.

To begin you need to ask yourself the following questions for each of your main characters:
What frightens them?
What motivates them?
What do they care about?

In other words, which character archetype are they? This basically means the pattern of behavior commonly found in a certain group of people. There are numerous character archetypes but each of these can be broken down into hundreds of sub-categories, which you can use as a starting point in your creation of unique believable characters. 

The following are a few examples:

The Investigator: They love to solve problems and have a very inquisitive mind. They are determined, intelligent and creative. They only trust a handful of people. They are deep thinkers and are great people watchers. They prefer to be alone and do not enjoy parties or huge gatherings. 

Reaction to conflict - They will not jump to conclusions or fly off the handle because they prefer to contemplate all the options before deciding on the best action. 

The Individualist: They are also creative and deep thinkers but they are very sensitive characters who care greatly what people think of them and their need to be liked is huge. They believe no-one knows them well enough to love them. This causes an inability to handle affection from another person so may seem aloof. 

Reaction to conflict - They are dreadful at handling conflict because they do not focus on solutions, instead they will bring up the past. 

The Sage: The wise person who always seems to know what to do in a crisis. Sometimes a mentor or teacher but always there to assist the protagonist in their quest for justice. They love to study and gain knowledge but they have a huge problem with procrastination.

Reaction to conflict - Their need to share their wealth of knowledge on a given subject may make them appear a know it all. They will also not be willing to see another person's point of view.

The Reformer: These are perfectionists with a desperate fear of failure. They are determined to do what is right and have very high standards and principles. They are rational and make excellent leaders. 

Reaction to conflict - They thrive on conflict because they believe they have the only solution and woe betide anyone who disagrees with them. 

The Challenger: They are extremely protective of those close to them and themselves. Very confident characters who will take the role of leader and are great at making quick decisions. Those who come into contact with a Challenger will have no doubt where they stand on any particular subject.

Reaction to conflict - Leave everything to them and they will find a solution

The Loyalist: Everyone would benefit from having a Loyalist fighting in their corner. Trustworthy and responsible. They choose their circle of friends carefully and do not handle stressful situations well.

Reaction to conflict - They do not handle conflict well as they are very insecure and will become paranoid, thinking everyone is against them. 

This should give you a great start to develop your own unique characters but remember as you create your characters, allow your imagination to flow and trust your gut instinct.