A friend of mine likes to choose a couple characters from TV and combine them in unique ways. This particularly helps if he gets stuck while writing later, since he can go watch an episode of TV, which almost always helps him get rid of writers block.
Others will do interviews with their characters. I find that this can work if the questions are both interesting and open ended enough.
Another option is a list of likes and dislikes. This can come in the form of favorite foods or colors etc. I don't find this as useful since it doesn't really show off the inner workings of the character. That doesn't mean it can't be relevant occasionally; a character might hate gravy because their parents argued about it as a child. But it's not always the best use of my time.
The last option I'll talk about today is designing a character like they're from a role playing game such as DnD. I mention that one because it's the most well known, but I personally love using the hindrances page from Savage Worlds. It's a list of things that were designed to affect a character in a way that will affect game play. As such it feels almost inevitable that these choices will affect the plot, thus creating more tension and interest.
How do you design or learn about your character?