Pay Attention To The Signs

Squinting your eyes is a beneficial way to observe your subject matter. It helps to simplify its main elements while eliminating unnecessary details. It enables you to concentrate on what is important, especially in the early stages of blocking in a drawing or painting. Larger shapes can be broken down more easily. Even in the later stages, squinting helps to keep you focused on what is important for your work.  

Methods of Squinting
While viewing your subject, close one eye, leaving your other eye open to squint down with. Some find it easier to squint using both eyes. The advantage of one eye being completely closed is that your binocular vision is shut down. This has the effect of flattening out the scene before you. When using the one eye method always close the same eye, don't switch back and forth. Please note that squinting in this way is something to be done at regular intervals throughout the drawing or painting process, not constantly. 

Visual Simplification
Squinting helps simplify the values, colours, and forms of what you are observing, enabling you to focus on the overall appearance of your subject without being distracted by the details and translate that information more accurately into your drawing or painting.

Squinting in Practise
Below, the left-hand image of the heron is slightly blurred to simulate the effects of squinting. Note how the feather and foliage details have now "disappeared" leaving only the larger shapes and values for you to work with. Squint at the right-hand image of the heron to see how your eye simplifies visual information. There is a difference between your eye and a camera.

Practice the art of squinting daily. Do it as you observe people, objects, and scenes, so it becomes more and more natural when you are drawing or painting.

Squinting has been used for centuries by artists to aid them in more accurate drawing and, it is a great technique to add to your sketching skill set.