Brightness, contrast, and hue and saturation can help to improve photos with just subtle variations in Photoshop. To increase Saturation, select menu item Image - Adjustments - Hue/Saturation. Photos used in the media and particularly advertising commonly have higher saturations so that they stand out from the rest of the images that we are bombarded with. Some photos just out of the camera may look flat and need some boosting. Instead of changing the saturation of a whole images, sometimes it may be better to change the saturation of a selected portion of the photo. Use a selection tool such as the Magic Wand or the Lasso tool to select parts of the photo on its own layer.
You can change the Brightness and Contrast in Photoshop by clicking on menu item Images - Adjustments - Brightness/Contrast. With Preview ticked you can see the changes as you are making the changes with the slider controls. When you are happy with the brightness and contrast adjustments, click on the OK button. If you want to see a wide number of preset adjustments then Variations will help you to decide which changes that you may need to make. Go to menu item Images - Adjustments - Variations and the Variations window will open up. You can change the highlights, shadows and midtones according to more or less of a number of parameters.
You can also recolor images and parts of images with Photoshop. Start off by stripping the digital photo of its colour by going to menu item Image - Adjustments - Channel Mixer and tick the Monochrome check box. The resulting photo may look a bit flat so you can put some contrast back into the image by going to menu item Image - Adjustments - Levels and sliding the changes until you are happy. Now make various selections using the Lasso tool for example and using a separate layer for each selection adjust the colour and contrast with the Color Balance Window.
If you get dust or small marks on your digital photographs you can use the Clone tool or the Healing brush. To make a foreground colour temperature look correct, you can adjust the photo with the Colour Balance tool. Go to menu item Image - Adjustments - Colour Balance to adjust the level of the colours. You can add more Red or Blue for example to get the exact hue to the photo that is desired. If you want a warmer picture you can add more yellow and/or red.
In Photoshop using Curves on photos can improve contrast. Click on menu item Image - Adjustments - Curves to open the Curves dialog box. The horizontal line of the graph is for the intensity whereas the vertical line of the curves graph shows the adjusted output values. Moving a point on the graph upwards increases brightness and moving it downwards makes it darker.