On my first novel (that never got completed because I can fully admit it was sh*t), I spend months on the backstory. I loved the backstory. I had every detail and names and places all figured out. I then spent another few months scrambling to make an actual story out of the backstory I had created. I felt married to the backstory. I felt like my plot had to conform to the elements of the backstory. Turns out (for me anyway) when you have a more interesting backstory then actual story then there is a problem. If the backstory is more interesting and has more conflict, then why not write the backstory? I have since scrapped that manuscript, written shorts for a few years, and am now back in the saddle with planning a new novel. This time I'm planning the plot first and adjusting the backstory as needed. This is working out much better for me. I can change the backstory however I want in order to make the current plot more interesting… Oh, maybe it would be cool if her guardian was actually the lawyer that condemned the bad guy to death and saw him executed, that would be a cool connection... Oh, maybe I should have it so that before…. her mother…. ohhhhh, yes… so that would mean… Etc. Do you do backstory first? Or do you work on it as needed to suit the needs of your plot?