I may have some an old book that could help, but I need to know the version. Two things that I normally adjust are levels and Unsharp mask (USM). When you select levels, you can try auto levels, but I usually just play around with the various colors spectrums.
I use the sharpening method prescribed by Scott Kelby - and he says to sharpen every image. Here is what Scott recommends.
1. Go to Mode and select Lab Color
2. Go to Channels pallette and click on Lightness Channel.
3. Go to Unsharp Mask Filter and set it to the following: (do this step twice!!!)
a. for People - Amount 150%, Radius 1, Threshold 10
b. for Cityscapes, Urban Photography or Travel - Amount 65%, Radius 3, Threshold 2
c. for General everyday use - Amount 85%, Radius 1, Threshold 4
4. If the image appears too sharp, go to Edit menu and choose Fade Unsharp Mask - lower the Opacity slider to around 50% to reduce the
strength of the second sharpening to 1/2 strength.
5. Go back to the Image Menu and under Mode select RGB color.
Sometimes if the image is sharp after the first sharpening, I skip the second sharpening and don't Fade it.
I forgot to mention that this is the last thing I normally do during Post Processing.
Be sure to let us know the version you have.