Design mountain lines on your paper as in the picture—bonus point to be inspired by your favorite hiking places!

Get two blue colors ready
Take one blue (I used ultramarine, but anything works) and add white to make a lighter color for the sky. Colour the sky above the mountains.

Take another blue (I used phthalo, but, again, anything works!) and add it as on the first, closest, layer of mountains. The mountains that are closer to you will be darker. This helps to create perspective and depth.

Add a little white to the same blue you used in the mountains and add it to the next layer of mountains.

Blend a bit more white in with your blue and add it to the next layer of mountains. Repeat with as many mountain layers as you have.
Enjoy! Bonus: add a bird/other animals in your landscape.