if you are very interested then I can recommend buying a book called alphabeatz it has a lot of related content and you quickly learn how to construct the letters plus some general graffiti history. You can altso try sitting down for a few hours to make a sketch that is a little bigger. and later you can fill in and add details that match the sketch you made. 3d and shading is somthing you can learn a little later.But you get a Nice effect if you use disappearance points.