Start by drawing the ridgeline of your mountain range, this should be fairly jagged but you can draw a softer ridgeline if you’d prefer. You should also include some lines branching off from your main mountain line.
Draw in some more, thinner lines branching off from your range, and, ridgelines.
Draw in some more lines branching off from the lines you drew in step 2. Your mountain range should kind of look like veins in their structure.
Finally, draw in small lines along some of the ridgelines you have previously drawn in. These are to add detail to your mountain range.