Create a very impressive drama effect, by adding rain.

First open your picture. I used the picture made with the Dark Landscape Tutorial.

1. Create a new layer and fill it with black with the Paint Bucket tool. In menu Filter > Noise apply Add Noise, choose Gaussian and Monochromatic, 10 or 15 should suffy for Amount. Go in Image > Adjustments > Levels and tweak it to erase some noise and to make it more visible. Finally in Filter > Blur apply a Blur Motion, which simulates a basic rain.

2. Change the Rain layer mode to Screen mode in order to blend it in the scene. Play with the opacity of the layer to adjust it with your scene.

3. Repeat the creation of a second Rain layer but with a little more noise to get a denser rain. Lower the opacity of this second Rain layer to simulate the rain in the background.

4. Now one will create large water drops on the image as if the scene was seen from behind a window. Create a new Drops layer filled with black, add noise.

5. In menu Filter > Pixelate choose Crystallize in order to obtain large crystals of noise instead of the small points.

6. Adjust the number of crystals in menu Levels.