Using shades of color are essential when I create glossy buttons and icons. In the Glossy Buttons and Web 2.0 Stickers tutorials, I used Cyan because it was easy to enter a percentage of Cyan, giving me quick shades. What if you need lighter and darker shades of a mixed color? An easy way is to hold down the Shift Key when you are dragging the sliders in the Color Panel!
The Pencil and Brush tools are useful, but sometimes frustrating. I always found the open paths it creates particularly annoying. A simple solution is to press the Option/Alt key when you are ready to close a path. Once pressed, it will join the first and last anchor points with a straight line. Holding down the Option/Alt key and drawing a little past the starting anchor will close the path automatically.