Adjusting Levels

One quick, fantastic way I've found to edit pictures in Photoshop is to manually adjust the levels. Under the 'levels' adjustment are RGB, Red, Green, & Blue adjustments. Some pictures may only take a quick tweak with the overall (RGB) others - like the following photo - may take adjusting one or more other colors as well

The original is just a bit hazy, and a little too blue (not enough red in the little girl's skin tone)
After the first 2 fixes, it didn't look as green as it should, so as you can see I also adjusted the green level.

This next photo was just too dark...
Just by changing the RGB levels, we brightened up the whole picture. Adjusting the levels is also a great way to make the eyes 'pop' a bit without doing anything else to them.
Though the little girl's face is still shaded, the bright background evens it out & makes it a fine picture. So, as you can see, adjusting the levels can make a huge difference in some photos.

In the same respect...
Other times the difference is very subtle (click to enlarge pics)
The adjusted levels in this picture made the little girl appear less hazy, and it also made the wheat more defined.

There are so many ways a picture can be adjusted with using only the levels. Though it's SO tempting to just hit 'auto levels' (or auto contrast / color) trust me - it's almost always better in the long-run to manually adjust the levels.