Attention to detail
If the composition is realistic, it's good to pay attention to details, for example scale, reflections and believability of the scene.
Characters
When using 3D characters, make sure they're posed naturally and creatively.
Compression
Avoid banding and compression.
Depth of field / focus
Avoid excessively shallow depth of field.
Make sure the main subject is in focus.
Use full focus when uncomfortable with a shallow depth of field setting / Use full focus alternatively.
Excessive noise / over-smoothing
Avoid excessive noise and over-smoothing.
Use Denoise carefully.
Use production-level rendering methods.
Repetition and simulations
Avoid simple repetition of 3D assets.
Or Make sure that the repetition projects are used for up to 10% of images submitted to the brief.
This technique can also be used very creatively.
Similar
Ensure renders are not duplicates or similar to existing content that you have submitted to Unsplash.
Text
Avoid use of text wherever possible.
Usage of assets
Avoid using isolated models on simple backgrounds. When using second-party assets, ensure they're a detail in the scene and not the main subject.