The trick of Photoshop is to make it look like you didn’t do anything. I was working on a catalog cover and I wanted to use an image of a dove holding an olive branch as the main image. Most of the images I found were just so-so—most didn’t have a dove with a wide wingspan, some had awful backgrounds, and none had background big enough for my purposes.
That may be the thing I do in photoshop more than anything—extend backgrounds. I always work in layers and masks and I always do more of the background than is needed (the image below is cropped even more than the original. So I found a dove from my stock site that would work. Then I added a layer to paint on more clouds and sky, added an olive branch into the doves mouth, and (after some constructive feedback from my bosses) increased the contrast between the dove and the sky.
The final result is subtle and hopefully looks like it wasn’t messed with too much.