Levels
First thing you want to do is go to image>mode>levels. Now you can do auto

levels but sometimes it will make the photo look worse. You will see a graph

and and there sliders (black, grey, and white). Now you want to move the

black and white slide to encompass the graph. See pictures.

 

Before:

 

After:

 

 

Exposure
Go to image>mode>exposure. Adjust these sliders to make make the best possible picture. The offset and gamma sliders usually don't need to be adjusted. If you adjusted the levels correctly you usually don't have to adjust anything.

 

 

 

 

 

Color Balance
Go to image>mode>color balance. If there is to much of a color drag the slider away from that particular color. Now if your photo lacks vivid color or even has to much go to image>mode>curves. If it doesn't have enough color bend this line up and to the right. If theres too much, bend the line to the bottom left.

 

 

Contrast
Go to image>mode>contrast. Brightness should be fine. Adjust the contrast a little to give it punch, but not too much or the image will look poor.

 

 

 

Sharpening
You can sharpen areas by using the sharpen tool but you can sharpen the whole photo by going to Filter>sharpen>sharpen (more). Use this to give blurred and out of focus images more definition.

Remember, by apply these filter, the image quality will decline a little. The more you sharpen or the more you add contrast, the more the image quality will decline.

Discuss the Adobe Photoshop tutorials on the forums. You can find the photoshop files to download there too.