Anything can be made into a moody picture. Even a bright summer day. It's of course easier if your picture already has some natural moody elements such as stormy skies, windy landscape, or impressive light. There's tons of ways to both enhance and create a moody scene in photoshop and to even just add some drama. It doesn't even have to be a landscape picture, it can be a portrait as well. This article is not gonna take you step by step, but rather give you a few ideas and starting points. In the end it all comes down to what fit that exact picture, you have to experiment.
When I create moody pictures I mostly follow some "rules". We want a dark almost eerie atmosphere, we want cold or atleast subtle tones, we want dark skies and sharp details and we want an impressive contrast.
For a moody picture we do not need unnecessary and distracting details that we can easily clone or crop away. Try to imagine standing on the scene, step into your picture. How would you like to frame it? What parts do you want the focus on and what parts do you not need? If it's details that can be erased using the cloning brush you do not need to crop that part unless it would look better to do so. I often end up cropping in different ways in multiple copies of the same picture and then putting them side to side to see their strengths and weaknesses.
2. Tonal range and contrast
For a moody picture we would like both details AND a good contrast. This can sound tricky since adding darkness and contrast tend to blow away and darken some parts TOO much. So what I do is that I even out the lights and shadows before messing with the contrast. A very quick and effective way to do this is to use photoshop's own "shadows and highlights". (image-adjustments-shadow/highlights). You have complete control over both the shadows and highlights, you can choose to darken as well as lighten them and still keep the harmony. You want extra details in your shadows, as well as stronger details in general, especially in your sky. After you are done with that you can either 1, go to levels and mess with the slider. Remember that you want CONTRAST. Or 2, double your layer and set it to OVERLAY as a blend mode. You can even slightly blur this layer if you want to add a little bit of dreaminess, but remember that your details won't be as eye popping then.
3. Darken the sky.
Easiest way to do this is a combination of using curves/levels and a layer mask. You want to darken the sky enough for some extra details to appear but you don't want to make it TOO dark. Remember that you don't have to apply the same amount of effect on the entire area, that's where the layer mask comes in handy.
4. Balance the light.
You want the light to fall where the pictures focus point is, where you want your viewers eyes. Putting it in the middle is the most common way of balancing the light, and you then darken the surrounding area like a soft wide vignette. Add some extra darkness on the four edges. What I like to do is to duplicate the layer and put it on multiply and then with the layer mask I erase the parts i want the light to fall.
First step is to lower the saturation. After this step you can take many directions. For example you can go for an old time rusty red/green feeling. It can give a very interesting effects to dramatic picture, kind of like a moody autumn with a spin. For this effect you change the color balance, either by only using mid tones or both highlights, midtones and shadows. You want to increase the yellow and red tones first. After that you can add some deep green, either by color balance (try it only on the shadows and so on) or by a color layer on top of the original layer, put on low opacity on any blend mode.
If you want the more traditional cold tones you can follow the same rules but with the blues, cyan's and magenta's. Again, you have to experiment, and in photoshop there's always many different ways to get the same or similar results.
Selective color is my favorite to use when i want to enhance or change ONE or multiple similar tones without affecting the entire picture.
6. Detail popping.
What you can do now is to go back to shadows/highlights (IF needed) or simply duplicate your layer and put it on hard light (or similar). Then you add a high pass (filter-other-high pass) in any strength you like. This will sharpen the picture and make the details pop and it's my favorite way to sharpen my images. Remember that sharpening is your LAST step. If you aren't happy with the effect, the final step would be to go to filter-sharpen-unsharp mask. You can play with the radius for some very interesting, almost hdr like results. Just do not take it TOO far.
7. Black and white
This is a very optional step, but on some pictures it's very flattering. Go to channel mixer (monochrome) and play around with the black and white until you like the result. If you do this on a duplicate layer you can lower the opacity to add back a little color.
Have fun experimenting!