When photographing landscapes with big portions of the image being the sky, correct exposure is not trivial. Usually the sky is much brighter than the rest of the image. If leaving the camera on automatic exposure, what usually happens is the land gets a correct exposure but the sky is overexposed and shows white in the photo. A white sky is dull.
How to compensate for this? One way is to use HDR technique, with multiple exposures and combining them automatically or manually through Photoshop. It is a lot of work and it does not succeed always due to wind moving the trees, waves etc. Best results are when everything is dead still.
I have a simpler technique, one needs a camera with a good dynamic range. Any modern DSLR is OK. I underexpose the photo by approx 1 stop. This way the sky does not loose the information. It is more correctly exposed while the rest of the photo is underexposed and turns out dark. It is easier through post-processing to fix an underexposed image by adding more brightness than the other way around, darkening overexposed parts. This is what I do for a quick fix of the exposure.
1. Copy the original Background layer.
2. On the Copied Layer Increase brightness until the land is properly exposed. (sky becomes overexposed but that's OK)
3. Add a mask layer to the background copy.
4. Create a gradient on the mask layer so that the sky image comes mostly from the background (original) while the land comes from the brightened background Copy.
Using the gradient will seamlessly make the transition between the two layers and the resulting image is better exposed