General image improving tips

To improve contrast and soften image - Before and After
Step 1: Open your picture in PS. I chose this one randomly from Last Beautiful Girl
Step 2: Go Image > Adjustments > Auto Contrast. Your image should now look like this.
Step 3: In my opinion it still needs some improvement, so I duplicate the background layer (right click on the layer in the layers palette, and click Duplicate Layer), and set it to soft light.
Step 4: Your image should now look like this. If you think it's too much, you can tone it down by lowering the opacity of the soft light layer.
Step 5: Flatten the layers (Layer > Flatten Image). If you think the image looks too rough now, this is how you can soften it. Go Filter > Noise > Median. Set the radius to 3 pixels, click ok. To fade the effect, click Edit > Fade Median. I changed mine to 25% opacity, but you can set yours how you like.
Step 6: This is roughly how your final image should look.

I hope you find this tutorial useful, and feel free to email me or tag me if you have any comments about it.