It's in the comic strip. The current arc has it where his daughter was kidnapped by these mob guys who want to hire Sandman to rob a bank and defeat Spiderman for him. Sandman doesn't want to because he's gone straight, which is why Peter has the dilemma where Jameson wants him to get pictures of Spider Man fighting Sandman (for....some reason). So he decides to show up at his house and ask him. Smooth.
Oh yeah, he also works a job at a diner. Which you get to see. It's quite awesome.