That depends on what desktop apps you are interested in using, such as litestep, desktop x or etc. If there is one you are specifically interested in, let us know and I am sure there are a lot of people that will help you and point you to some good tutorials. If you are new to the shell apps, definetly read the manuals first. That is probably the best advise anyone can give.
Other than that, figure out what is the most important things for you on the desktop, the apps you run the most, then put together a rough layout of the graphics style you want. From there you can customize the rough graphic to fit each app you use.