Did a quick photoshop session on an old cat picture from my “Stray Cat Series” on flickr.com/KalDesigns.
What I used for this was mostly color fill layers and few minor adjustments to curves and saturation.
1. Color Fill
This can be done with either making a new layer, filling it with a color you like or sample a color from the image, which is what I did. What I usually do is sample a darker and lighter color in the image and set one of them as a darken layer and the other a lighten layer. Turn down the opacity and layer mask to your liking.
You can create a similar effect as the color fill method by adjusting the RGB in curves. Adjust for color, lower opacity, layer mask, and so on.
Vignette can be done easily in lightroom but I didn’t feel like exporting it to lightroom then importing it back into photoshop. There are so many ways to do it, but what I did was create a new layer, center elliptical marquee tool, invert selection, feather it by whatever you want in refine edge, and adjust opacity.
Another optional thing you can do is add a texture layer over the image and change the layer to either overlay and screen. Like Instagram’s toaster filter has kind of a crosshatching effect in the middle layer, you can easily mimic that with anything, say a macro shot of cloth or a piece of scratched glass/metal.
Everything is subjective, there are countless things you can do to enhance your images, but the key thing to keep in mind is to not overdo it to a point that looks over-processed.