This is a small overview of how to enhance underexposed pictures.
Very often, when taking snapshots without a tripod and bad lighting, I'm quite dissappointed of the result. But there's still hope for your picture! See this:

Final DA: [link]

Original: [link]

So what do I usually do to get a better exposure with this?

1. Open Phtoshop (you already guessed this, right?)
2. Add an adjustment layer "levels" and edit the levels, so you get an lighting that you like, not too bright, have an eye on the details, in this picture I didn't want the midtones of the fur to vanish.
Then you want enough blacks, so the picture doesn't look grey. With this adjusted, I play with the mid-slider and eye-measure.
3. Remove noise. After doing step 2 you will notice very much colour noise, which ruins the pic. Why not take advantage of technical prgress? After reducing the noise as much as necessary and as less as possible you can go ahead and
4. Sharpen the pic again.
5. After step 2, there will probably be some weird colour-shifting going on. So you can now add an adjustment layer hue/saturation and play with it. Don't just desaturate unwanted colours, for you will get noise again. Be very gentle with this one and also play with hues and lightness. Example: I have yellows in that pic that just don't fit. So desaturate yellows just a little and pull down the lights for this a bit.
6. Still work for us to do. You will probably still have some noise, that distracts from the subject. Now comes a neat trick, that somehow gives the pic some kind of "film-look". Go ahead and copy all to one new layer and add gaussian blur to this, not to much, but enough to see a difference, it's a question of practice. Ok, now choose the blending options for this layer, something like "soft light", voila! Makes the picture much softer without loosing details. Go ahead and try different blurs and blendings, sometimes "colour dodge" or overlay works better, depending on the picture.
You can play around with the layer opacitiy to get a better result.
7. If you are still not satisfied go and add unfocused areas, as I did in this picture. It works like this: Copy all layers to a new one and add a lens blur to this. Now you can gently erase out all parts of the pic that you want to be focused.

Step 8. Ask me about details or leave a comment or just use this technique to enhance your pictures

Cheers
Bernd