Here is an example of a photo that I took on my cell phone.
The first thing I do to every photo is make a duplicate layer and apply an unsharp mask.
I keep the threshold at 0 and depending on the resolution of the image, keep the radius between 1 and 3 pixels. The amount is entirely up to you.
Next, I adjust the curves and usually increase the contrast by applying what is called an "S Curve". Youll have to play with it a little bit to get used to how the curve works but it is a powerful tool for adjusting the light in a photo.
Lastly you can make a new layer and fill it with the color of your choice. set the blend mode to overlay and drop the opacity until it looks the way you want. This is a nice, simple way to give a warm or cool feel to an entire photo.
And that's it! those are three easy ways to enhance any photo! be sure to play around with settings and experiment to find a look you like.