I have an intuos3 9x12 but I started with a really small cheap thing. I found with the small one that it helped to find exactly the right alignment of the pad on the desk. 

In your paint program, close your eyes and draw a few straight vertical lines and a few straight horizontal lines. Now look on the screen, are your lines really horizontal and vertical? Probably not. If they are a bit rotated, rotate your tablet slightly and do it again. When you find the position where your natural body movements give you what you want on screen, mark the position of the tablet on the desk with tape or something. Place it there every time and it'll cut down the learning process.