For large walls have one single art or two but not more. Try to have both of them of similar size to maintain balance although the orientation maybe different – One portrait and one Landscape. This also helps to break the symmetry.
Generally, have artworks contrast with the color of the wall. For dark walls try to avoid dark paintings. If you wish to have a dark painting which you are in love with and have dark walls ensure the painting is well lit and highlighted.
Leave some breathing space between the edge of the walls and the frame of the painting. Leaving at least 1 foot on both sides is desirable.
Avoid having other elements on the wall where you are putting your painting. You don’t want the focus to shift from your prized possession.