it's not just about sharpen and contrast.

exposure - sometimes you need to lighten or darken certain parts of the image

color - too much here. slight colour tint in shadows, another tint in highlights, individually adjusting hue/saturation/luminance of certain colours only...

composition - i think shooting slightly lower so that the left rocks are higher than the horizon would make it more interesting.

compositing - photoshop in more dramatic clouds

dont worry bro, a lot of ppl take years and years to produce professional results. Im still learning myself. Youtube is your friend.

Ah I didnt realise you were using the Sigma 18-35. Should've spent the money on books or classes first bro.

At least one good thing you did was ensuring the horizon is level.

try taking the same photo again but during sunrise or sunset (google "Golden Hours"). you'll immediately see a big improvement there.