We like to discuss game related topics in this forum, but keep in mind that this forum is actually for support on the SFML library. So I'm not quite sure if you're question really fits in here and less sure if many of us (programmer) can give advice on art creation (usually done by artists)...
Maybe you should check out an art community and asked there, also to me it doesn't look like such a trivial task and I guess there are many diffrent ways to do it, so don't except a guid that will walk you through step by step. Art creation is a process that has to be learned or be given.
But hey maybe someone knows about stuff like this in here.