Visual triangles are a good strategy. The idea is that if you have 3 things in a similar or the same colour or 3 items that look similar placed at 3 points in a room, it causes the eye to travel between them and creates a kind of balance. It doesn't have to be a perfect, even triangle, either. It's typically pretty subtle. As an example, if you put 3 plants in a room, put one by the front door, one on a side wall and another along the back wall somewhere. Or if you have, say, a room that's mostly green but include a lotus lamp, a hibiscus and a a pink cushion on a green chair and place them at different points in the room, the viewer's eye will pick out these hints of pink. Or birds on the ceiling - a group of 3 together, or 3 spaced around the ceiling, or 3 clusters of 3 all work well.