Colour

I like colour in a photograph, it doesn't have to be 100% saturated. It conveys warmth or coolness, time of day and emotion. There's a special time of day called the golden hour, when the low directional light of the sun has a softer and more dramatic effect than the harsh midday sunlight.

Colour theory is based on painting history but can be applied to photographs as well. Some lucky people know instinctively which colours go with others, most though have to learn. There are colour harmonies, opposites, complementaries etc and it takes time to sort out what colours are suitable for foregrounds and backgrounds, so they they do not jar and distort the perception for the viewer.