This one really only has like three steps, so I can talk you through it.
This edit is primarily for outdoor type scenes, or any type where you have two pretty defined areas. Or not. It just depends on you.
Open your photo and do some basic editing. Then go to Layers>New Fill Layer>Gradient. Make sure it is set to Linear and then adjust your angle so that it goes with the flow of your picture.
Set your colors, really any colors you like will work.
Change the gradient layer blend mode to OVERLAY, and then click on the white box in the layer where your gradient is. (and hey look! you can see the actions I use to resize and sharpen my pictures for the blog and Facebook. they’re by MCP Photoshop Actions & Lightroom Presets)
Select a small brush and change your primary color to black and then color over your subject and any other important spots so that their coloring and lighting doesn’t go whacky.
That’s it! The edit is all done, and seriously once you get the hang of it it takes like maybe five minutes to do. I spend more time on changing/picking my gradient colors than the rest.