I like to start with traits - for example, Eileen is brave, resourceful, and rebellious. Those three words alone give you a good starting point for portraying Eileen. Getting your characterisation right is everything in getting the story right (and therefore give it much more chance of being accepted somewhere). A good plot needs great characters to make it work.
It is useful to outline a character whether you put all you detail into a story or not. (The likelihood is you wouldn't. I know I need to know this and that about a character, your readers might only to know "this"). However, outlining a character gives you all the information you need to work out what kind of story they would be in, how they would handle a situation (or mishandle it), and what their "happy ever after" ending is likely to be. It is then up to you if they achieve it! (Great stories can be found in a character attempting to get to this point but never quite making it so they have to adjust their "happy ever after" for something more sustainable over the long term. I guess this is where the "happy for now" endings, especially in romance novels, comes from).
I've found it does pay to take time outlining. I find when ready to write the story itself, I write it quicker because I've already got the "building blocks" in place ready to go with my tale.