Once you have your character sitting right there in your head, all you really need to do is wind them up, put them down, and simply write down what they do, say, or think.
Terry PratchettAnd at the other end of the bar the world is full of the other type of person, who has a broken glass, or a glass that has been carelessly knocked over (usually by one of the people calling for a larger glass) or who had no glass at all, because he was at the back of the crowd and had failed to catch the barman's eye.
Terry Pratchett