Take some time to look at these files. You can download them via this link (below). They are files done for a project similar to to making an Avatar layout. These files will help you understand 2 things. Firstly: how to use the layers in Illustrator; and secondly, you’ll see a style of ‘artwork’.
You should now have some skills in illustrator to start getting the ideas developed. The recommended Adobe tool for doing this is Illustrator. But of course Photoshop is also useful. But because you’ll be using Flash next semester, it’s better to start using Illustrator.