Pillows on a couch are usually the last piece to finishing a room. Every photo you see has a different arrangement: matching, even numbers odd numbers etc., making it difficult to know which will look best in your space.
I created a little cheat sheet on some common pillow arrangements. Which one you choose depends on the space and your personal preference.
The first one is Mirror Symmetry. This is where each side mirrors one another and are normally in in even groups. This pairing is more of a proper look and will work great in traditional homes. With this look the larger pillow will match and the smaller pillow will match.
Asymmetrical and Odd Number pillows work great in more relaxed home like eclectic, boho, or modern homes. You can mix or match any patterns depending on the space.