Photoshop is fine but only if you know what you want to exactly draw and you know the details of how its going to look. What if you don't have an idea and you need a starting point to really have your art take off? what if you want to train or exercise your brain in order to create a whole new level of creativity? here is a great program to use http://al.chemy.org/ it gives you a great starting point to sketch your idea. Here is an example of how to use the program and how it works.