You've got a nice sense of composition, cool!
Yeah, besides Ramalooke's tip, for landscapes I can say also that you could do the sky and the - I forgot the exact word in English - floor first. After this you'll already have some of the most important colors of the composition, and will be able to pull the atmosphere effect easier, relying only on opacity to get it's the main colors.
Having the main colors of earth/forest/snow/grass, whatever covering the horizont line of your composition will allow you to think in the best colors to mix with it, to add some visual interest and others to contrast with this, to render the light and shadows.
Well, it's not like I'm experienced with landscapes, I just started studing this, but working this way was effective for me.
P.s.: I hope this post doesn't land on moderation too. >.<