The shape of the wall needs to match with the shape of the painting. A rectangular wall needs a rectangular painting. A square wall needs a square painting. It is essential to look at the dimensions of the wall and then choose the painting size. One can break the empty space on the wall by putting 3 or 4 small paintings, they can be arranged diagonally or they can be arranged in a row or they can be arranged in a square formation. Match the space of the wall with the size of the painting to get the best effect. But there is no stopping lateral thinkers so keep doing your own thing.