There are hundreds of ways in which to paint a landscape. If you are a beginner I would suggest that you do not start out too adventurous. Begin landscapes by painting tonally. If you paint tonally you will take into account the atmosphere of the scene.
What is tone? Tone is where a colour sits on a grey scale between black and white. Imagine you are watching an old black and white movie. In this movie you are not seeing any colours, all you're seeing is tone. If it is a Western then the bad cowboy will have a black hat and this will appear as a dark tone. The good cowboy will have a light colour hat which will appear as a light tone.
As you paint tonally you should notice that the greatest contrasts between light and dark are those in the foreground. As we move further into the distance the light and dark areas become closer together and less distinct until in the far distance there is very little difference between shadows and lights. For example: A red barn near to you will appear bright, there will be (on a sunny day) plenty of contrast between the light and shadow sides of the barn. A similar barn further away, perhaps in the middle distance, will appear less bright, the light and shadow areas less distinct. It is an easy thing to overstate the middle distance colour, especially if you are on location as your eye will see it as bright red. But on the canvas this will appear unrelated to its surroundings and draw attention to itself.
Objects in the distance are also less well defined, do not try painting too much detail into distant objects, often a few strokes of the brush create a more pleasing result than overworking. Trees and foliage are a good example. Take a good look at the tree(s) closest to you. A tree may appear predominantly green but on closer inspection you will discover a wide range of subtle tonal variation. Yellow/greens, brown/greens, grey/greens, red/greens and so on, and each of these will have a light and shadow aspect. There may even be reflected light if, for instance, the tree overhangs a pond or is close to a wall. In the foreground you can set about placing all those on the canvas. But what of the middle ground? Trying to accomplish all that variation in the middle ground and beyond will lead to a muddy mess. Instead look at the over-all tone of the foliage and mix the shadow component. Remember it should not be as dark as the foreground shadow.
Place this into the middle ground extending partially into the areas of light. Lastly mix the light component, again remember it will not be as bright as the foreground, and work this into the light areas and over the top of some of the shadow areas. Roughly blend the light and shadow edges but do not over work the two together.
Reflected light as I just mentioned will also have a tonal effect on objects. The bright red barn will likely cast a redish hue on anything near, a pathway for instance, but be careful again not to overstate the obvious unless that is your intent. Trying to mix some red hue into you path colour would likely be a mistake due to the mixing of too many colours, try instead to paint some barn red on the path first and then paint your pathway over the top once the underlying red is dry. This has the effect of the underly colour showing through in more subtle ways than by mixing colours alone and also helps keep the vibrancy of colour where the mixing of too many colours can lead to a loss of intensity. See Hue, Intensity & Tone.