Step One
With your image open, start a new adjustment layer: LAYER---> NEW ADJUSTMENT LAYER ---> LEVELS.
A dialogue box will appear and just click OK. The familiar Levels Dialogue Box will appear. For this image, move the right slider to the left. I moved mine to about 140. Notice that you are making the right side of the image as bright (light) as the left side was before we started the levels. Accept this change. In the next step we will apply a gradient to gradually "mask" these changes from the left while allowing them to be seen on the right!

Click next when you are ready.