On Contrast: be lazy and paint less
I am a lazy artist: I do not want to spend hours on complexity and I enjoy simplicity in a piece. The thirds-rule comes in handy here: you can create very atmospheric pieces by creating a strong contrast between complex areas and very simple areas of your painting. Let's take a closer look at the piece above:

As you can see, the better part (almost two thirds) consist of the sky which is basically a gradient. All the visually dense information lives only in the lower 1/3:

And of course it's not my laziness that counts here, but another way of using contrast in your composition: not only the tonal contrast you can use when applying colors to create create e.g. depth, but also the a contrast of visual density that can make a piece more exciting. 

The almost empty sky and the contrast of all the things to look at at the ground. The tripod aliens in the background and the empty swing in the foreground. The rising (setting?) sun to the right and the little village to the left.

Here's another piece that goes to even more extremes in omitting showing showing the ground of the landscape.

Give it a try: leave the better part of your painting empty and focus on only 1/3 of it. The thirds-rule can help you create interesting tension in your work.