One more thing, I have not tested this technique on animation, so I have no idea how well the cloth will look if Deformers such as Bones, Displacement and Dynamics are applied to this mesh. This is more a technique for still images but by experimenting on your own you might find a use for it in your animation work.

Some of the basic principles of making folds and wrinkles in clothing is to pay attention to the following:
1. Triangle Shapes - Try to shape folds and wrinkles with triangles in mind.
2. Fabric Type - The thinner the fabric the sharper the triangles will be while the thicker the fabric the rounder and smoother the folds will be.
3. FLOW - Pay close attention to the stress points of the cloth, where there is more stress the straighter the folds will be and vice versa, the less stress the more triangles.

The perfect example of this is the elbow (or knee with long pants) when wearing a long sleeve shirt made of a medium weight fabric. When you bend the elbow you will notice straight forming folds to the the back area of the elbow while there are more relaxed triangles on the front area. If you extend the arm you will see straighter folds going across the arm following the two stress points, the beginning and end of the arm.

Once you start thinking about these basic principles you can use whatever modeling technique you feel more comfortable with, Modeler offers plenty of different tools to add detail and geometry to a mesh but the tools I use the most for this are: Extender Plus, Supershift, Cut, Add Edges Edge Bevel and of course Spin Quad to change the flow of polys.

You might want to use your character in a background layer for reference and even use body parts to work from. I'm going to use an upper torso to show some of the different types of folds.