Images should convey immediacy, authenticity and life. Also make sure that they are gender balanced and normcritical to avoid stereotyping. Their composition should be straightforward and the focus clear.
The photographies should have a natural light. Indirect natural light with soft shadows is preferable to bright sunlight with harsh shadows. Backlight helps make backgrounds bright, simple and harmonious.
Skin tones should be soft and natural, i.e. as they would appear in indirect and naturally soft light.
Any photo editing should be subtle and result in a clean, natural image, as in the examples shown.