Translation of the original idea
I often struggle with taking a thumbnail and translating it into a full-colour render, while retaining whatever made me like the sketch in the first place. A certain level of disconnect between the thumbnail and the final art is unavoidable. The trick is to maintain as much of the sexiness of the initial sketch as possible, while creating a well-thought-out render. Don’t be a slave to the thumbnail, because it can almost certainly be improved. But find out what made you fall in love with it, and then try to keep that aspect in your final image.