One of the simplest processing tricks you can use is this:
Open your picture and add a levels adjustment layer. BUT ~ don’t adjust anything. Just add the layer.
Now, go to the Layer Mode drop-down box (at the top of the layer palette, Normal is the default). There are several different choices but I’m going to show you three I use all the time.
This is the picture with nothing done to it:
This is the picture with the mode set to Multiply, and the Opacity taken down to 25%. Multiply makes the image darker.
This is the picture with Screen selected and the Opacity taken down to 25%. Screen makes the picture lighter.
And this is the picture with Soft Light as the mode, taken down to 25% opacity. Soft light adds contrast.
You can also use Overlay to add contrast, it’s just harsher.
Using an adjustment layer in this manner makes it easy for you to fine tune your processing. If you continue on and decide you need the picture lighter you just increase the opacity of the screen layer. If you want less contrast you reduce the opacity of the soft light. And of course, you can use the layer mask attached so that it only effects the part of the picture you want it to (make the background darker with a multiply layer and make the face lighter with a screen).
So go play with your modes!
(This was my final version of the picture, with some toning added, which I’ll write about at another time…)