Start with what you know; yourself. Use your own psychology as a template for your character. It won't be autobiographical because your character will be experiencing different things, meeting people you've never met but only imagined meeting, and so forth. That's when it can get fun. The best way to make a character interesting is give them depth. If your character is deep enough, rich enough in thought and emotion, if they think and wonder about things in an intriguing way, then almost any situation you put them in will be interesting, but that ultimately has to come within yourself as well. A deep person can write about shallow people as well as deep ones; but a shallow person can only write about shallow people. As for wanting and needing, we all know what those are. What we want and what we need varies from person to person but what the feeling itself is like to want something and need something remains pretty much the same. So if your character wants to be a model, you can describe that want by simply harkening back to something you've wanted. Imagine something you've wanted really bad and you can describe what your character is feeling, it's just in her case the object of her want is modeling. But the feeling of want is the same. The same with need. The objects of need vary (and many don't, like food, sex, etc.) but the feeling doesn't.