Flowers rendered using Forest Pack tend to look dark and dull. This can be corrected by going to the diffuse texture map and turning off the filtering. Then go to the Output settings and increase the values to brighten the texture.
Try to make sure we can see details in shadowed areas. Example… brick pattern on the shady side of a building. Sometimes GI will obscure these details, but the right settings will reveal them.
Cars should primarily be black, white, silver, dark gray, with other colors in lesser amounts. Bright colors should be minimized or omitted, and not a distraction in the image.
Sun angle should be direct on 1 side of buildings, and shadow on the other. Sun should never be located behind the camera.
Skies should be photoreal. Not overly saturated. Little or no noise should be visible. Clouds should be “light”, not dark or threatening.