I put my big Wacom tablet directly in front of me on the desk, and place the keyboard along the top edge of the tablet, between the tablet and the monitor. Then I use my right hand to hold the pen, and my left hand to press keyboard shortcuts to choose tools, resize brushes, etc. My mouse is to the right of the tablet when I need it.
When I'm not retouching, the tablet slides out of the work space and the keyboard moves closer to my seat.