I'd plan out where you want the map to be, where the mountains or at least the most important areas will be, I like to use textures for a visual reference since they can be changed later.

I like to use the flatten tool to get a height reference but you could use wing it and use raise and skip that step altogether.

Make use of textures and various rock pieces, mix stuff around make it look natural, try to picture formations of rocks or trees, various dents and imperfections in the terrain, use raise and lower tools for this, it'll help give it a more natural flow (nothing in nature is perfectly flat), plus it'll help provide players with more cover.

Honestly the best advice i can really give is just practice it, if something doesn't come out the way you want, try something else.

Hope this helps :)