How to improve my rock formation sketch?

https://preview.redd.it/j3mazcdfswrf1.jpg?width=3024&format=pjpg&auto=webp&s=928d67e6c5db9b61706eb782497f9df7d3bcb801

I really mountains, and rock formations. The first one is just a blocky version, to help me practice visualising the forms without any detail or shading. The one below I am trying to shade and add some detail. Difficulties I face are:

1. For the rock faces that are in full light, what details can I add? I find myself just squiggling random lines on them to fill the blank space without understanding their purpose.
2. Maybe the straight lines are cool for the initial block sketch, but for a more detailed version, I should use more varied lines?

Thanks! The goal is to be able to sketch mountains during a hike.