The human brain has a strong tendency towards order and continuity. We instinctively dislike chaos, disorder and disjointed arrangements. Which is probably why we see so much linearity, repetition and equal measurements in buildings, urban design and such. But in the world of painting, this tendency towards order and equal measurement can cause trouble.
During my trips to Idaho to study painting with Scott Christensen, I recall him repeatedly talking about the importance of "variety." The natural landscape is full of abstract designs and irregular shapes. Rarely will you see two trees of the exact same shape and size. Nature has this delightful way or creating organized chaos. As a result, landscape paintings with repeating shapes immediately stand out as false.
When we are out on location, it's easy to get absorbed in the many facets of a plein air painting. The drawing, edges, colors, values, etc. The result is that we sometimes miss a repeating pattern or equal measurement. We just don't see it at the time. This happens in the studio, too.
If you want to craft better paintings and avoid repeating patterns, there are two tricks that can help you immeasurably: Using a mirror and turning your painting upside down.
I have a small pocket mirror that I carry in my backpack when painting on location. Once I've blocked in the basic shapes and design of my study, I pull out the pocket mirror and look at the painting's reflection. In my studio I have a large wall mirror behind my easel, so that I can view the work's reflection. It's amazing how much the reflection of our painting reveals blaring errors and repetitive patterns. Seeing the painting in this way greatly assists in uncovering a different perspective. From there you can identify the issues and correct accordingly. Be it a landscape, still life or portrait, the problems just become more clear in the reflection.
The second trick involves turning your painting upside down. When you do this, you tend to view shapes more clearly than with the upright image. As a result, uniformity and repetition stand out more. It's easy to implore this trick in the field or in the studio.
Even the most accomplished painters fall into this trap of painting unintentional patterns. The trick is to constantly look for them in your work and focus on variety. Variety of line, color, design and edges. But be careful about variety of values, because too many value changes can create a confusing and spotty picture.
Next time you venture out into the field, get yourself a small pocket mirror to use. And in the studio, consider incorporating a large mirror to view your work in. Scott Christensen has a large mirror on rolling wheels, so he can position it at various angles to view his work. These two tricks, a mirror and upside down viewing, will greatly assist you in spotting those annoying, repetitive patterns.