Molotov Everything - Layer Masks
Sid's original image!
Sid's final image, one minute later!

You can discuss this technique and ask questions on Digital Grin.
Click the background copy and change the layer blending mode to "Overlay".  The image will gain more contrast!
Some images only require this extra contrast. You can also change the opacity of this layer, thus the effect of the extra contrast by sliding the opacity from 100% to a smaller value. This will lesson the effect to the entire image.
This is where you need to finesse your image.  I create layer/vector masks and paint away the areas of the blended layers I don’t like.  

With the “background copy” selected, click the “add vector mask” button at the bottom of the layers palette as shown here.
For this particular image I used the gradient tool to remove the section of the “background copy” of the land only. Make sure you have highlighted the layer mask before using the gradient tool. Also make sure you are subtracting the layer mask when applying the gradient tool. * you can alter between subtract and add, by clicking the “X” key, and this works with all tools.
For different images I might use the brush tool to remove the effect of the background copy when there is not such a straight horizon.

The power of working in the layer masks with either the gradient tool or the brush tool is that it can be reversed or altered at any time so long as you keep your layers with your image. Painting the effect of each background layer on and off is simple and entertaining. 

Here are a few details that make it easier. I usually change the opacity of the brush to between 30% and 50%. I also change the hardness of the brush to 0%. To reverse the effect of the brush just click the "X" key, also to change the diameter of the brush use the bracket keys [ ]. 

For my final touch on this image I painted away some of the contrast in the sky with the brush tool in the layer mask of the “layer 1”.

Select the “layer 1” and create a layer mask. Then select the brush tool with a 0% hardness and large enough to cover a good section of the sky. Now lower the opacity to about 30% and paint away the effect of the “overlay”. This darkened the sky a bit which I preferred.  Note, the painted area in the image below will not appear, as I used it to illustrate about where I painted away the “layer 1” mask.
Now change the  blending mode to “Multiply”. The image will become very dark.
Molotov Everything - Layer Masks
Molotov Everything - Layer Masks
Molotov Everything - Layer Masks
See photo in original gallery.