Article Courtesy Scrapjazz.com: by Denise Gormish
Photoshop provides an endless array of ways to improve photographic images. I know. I have taken plenty of poor photographs and been able to turn them into something quite usable by editing in Photoshop. Two easy editing techniques are adjusting the Photo Filter and adjusting the levels.
Photo Filter
Have you ever taken a picture that turned out too brown or too blue? These two problems can be adjusted with the Photo Filter. Go to Image - Adjustments - Photo Filter. If the image is too blue, choose the warming filter. If the image is too brown choose the cooling filter. My photo of the coffee bag was too blue. I chose the warming filter to improve the color.

My photo of my dog was too brown. I chose the cooling filter.

Adjust the density to change the amount of color change. You could also chose a specific color if you want to adjust one color.
Levels
Levels allow you to adjust the brightness of an image. Go to Image -- Adjustments -- Levels. An image histogram will appear in the levels box. It resembles black "mountains" in a graph. Levels lets you adjust the histogram by changing brightness and contrast. The far right white-point slider will brighten the entire image. The far left black-point slider will darken the entire image. The middle mid-tone slider will adjust the mid-tones.
Most images look best with some part of the image dark and some part of the image light because it creates contrast. An image like this will have a histogram that stretches across the entire width of the graph. To get this effect, change the position of the black and white sliders. Adjust the lightening simply by moving the sliders under the graph so the white-point slider is under the rightmost part of the histogram and the black- point slider is under the leftmost part of the histogram. If your image still needs some help then move the mid-tone slider.
In my dark photo, I adjusted the right white-point slider to the left and adjusted the mid-point slider to the left.

Another way to adjust levels is with the eyedropper tool. It helps to set the white balance. This tool sets where the blackest point and the whitest point are on the image. To use the white dropper tool select it. Next, pick a point on the image that is white then click on it. The rest of the image will adjust to that being the whitest point in the image. The same process can be used for the black dropper tool.
With just two simple Photoshop tools your images can be improved quickly.