Character development for any novel should be a meticulous process. If you're thinking of writing a series of mystery novels revolving around your main character, you need to give him/her an even deeper background.
In the first novel in your series, you will use certain details from your major character's past to get things going. In each subsequent novel in the series, you will need other details from the past to renew interest in your character and in his/her part of the story.
Character authenticity is a necessity. To ensure authenticity, you need to know the details of your character's life. For example, it's not enough to know that he hates cranberries. You must know why he hates cranberries. Maybe the answer is that they taste bitter to him or maybe he's allergic and almost died from eating cranberry bread. Knowing why, increases his authenticity.
Before you can compile the background stories you'll need to carry your character through a series of novels, you need to get the basics down. Here are some categories that need to be addressed:
physical characteristics of your character
settings/locations (hometown, vacation spots, etc)
Make a list for each of these categories and add other lists that may be appropriate for your character. We'll move on to how to go about looking into the past of your character and significant life events in the next session.