When painting landscapes the things I do most are to squint while looking at my subject and while laying in my block-in and stepping back from my work at regular intervals.
Squinting while painting helps us eliminate details and focus on large masses and abstract shapes. This helps us keep our compositions clean, uncluttered with extraneous detail and effective. Nature is full of detail but we have to choose what tells our story and be judicious in what we include in our composition.