There are two main things that people often overlook with mountains (myself included sometimes) and they are spurs and foothills. What you have so far looks like a good spine but that spine needs some ribs sticking out (those are the spurs). They don't have to be long or tall or very pronounced but mainly serve to break up the linear look. Mountains then transition into foothills before finally descending onto the plains. Foothills are basically smaller versions of the mountains but with a green color instead of browns and grays. Desert hills would, of course, be tan and not green and polar hills would be white but you get the idea. Lastly, mountains slopes often have forests on them but that's a whole other barrel of monkeys. So what I would say is that you have a really good start, one of the best starts I've seen in a while. Just add some spurs and foothills and you should be a lot happier with it.