
In creating a back story, I find the easiest thing to do is to make a detailed Wiki or some sort of biography for your character. It really helps you to think of all the small quirks to his personality that you'll need to know, and it gives you a sort of guideline you can stick by in determining your character's actions, especially since you can look at it if you forget anything. And, of course, if it turns out you don't like some aspect of your character in execution, it is possible to retcon. Don't feel pressured to continue RPing something you don't like just because you wrote it down in your character's bio.
As to how to progress forward in your character's story, while some people like to have pre-planned plotlines, or intend for their character to somehow go from a Point A to B to C, etc., I like for things to be more free-flowing. Sometimes I get ideas I like to implement, but for the most part I find it easiest to go with the flow of the RP. Generally, I just consider my character's personality, and then decide where my character ICly would go from there, how she would react, what goals she would strive for, etc.
As to how to progress forward in your character's story, while some people like to have pre-planned plotlines, or intend for their character to somehow go from a Point A to B to C, etc., I like for things to be more free-flowing. Sometimes I get ideas I like to implement, but for the most part I find it easiest to go with the flow of the RP. Generally, I just consider my character's personality, and then decide where my character ICly would go from there, how she would react, what goals she would strive for, etc.