I used to have them first determine their stats for their character(s), then flesh them out, by doing a page or so detailing their characters' lives: i.e., where the characters lived, how they earned their living, what their education was, their hobbies, their friends and family background, etc.

This is what a writer calls 'backstory', and it lets you know what a particular character is likely to do under a given set of circumstances. This is a technique that can help you with your rp posts, as well. As a DM, I would sometimes penalize players if they couldn't account for their characters' actions properly. For example: a dwarf character who was orphaned and adopted and raised by a human family is not going to act or react the way a dwarf raised by a dwarven family would.