Admit it, you've always wanted to create a fictional life for yourself. It's why we become writers. Or, one of the reasons anyway. So we can make shit up and live in a world outside of the two slices of white bread we've been handed.
So here's your chance to really get creative.
Don't just invent one and two dimensional characters to conveniently fit your story. Create real, three dimensional people who have real lives. Before you write the first word or sentence of your new book, take one full day and create character bios. When was your character born? How much did he or she weigh? Where did he go to grammar school? High School? Who did he take to the senior prom? How many times was he beaten to a bloody pulp up in Juvy? That sort of thing.
You might not use a one-tenth of the information your create in the lives of your characters for your novel, but just knowing who they are, inside and out, will create a richer, more complex, more entertaining novel.
So tell me, who are you going to invent today?