Sundial, you have a point about not always being able to see what makes or breaks a picture.
As an ex-lighting-tech, I always worked on the idea that my contribution should generally be invisible. It was the greatest compliment when someone once said to me, " I realised it was getting dark, and thought ‘someone should turn a light on in that room’ and then someone came in and turned the light on" They had lost the sense of this being a set, and thought of it as a room with the sun setting outside.
To answer the original question, up to a point; It’s about getting all the details right. What makes something look ‘real’ is that there is nothing in the scene that says otherwise. If you cannot model it realistically, then don’t put it in. PLAN every part of the image/movie. How dark are the shadows, how rough is the metal, where is the light coming from ( light does not just appear from nowhere.) What makes a room look like a room is the reality of what is outside it. Even if you can’t see it, it’s still theoretically there, and your brain can deduce if it doesn’t make sense. I have seen many sets and CG images where the sun is shining in two directions at once, or things don’t throw shadows where they should.
Where is the ‘ship’ coming from, where is it going, why is it flying in a curve. Is that even possible at that speed? How big is the planet, or the sun, and how far. Still images can get away with a lot of fakery, but moving images have to be far cleverer.
Blender will certainly render a totally convincing image, or even movie. It still needs modelling skills, lighting and texturing skills, a good eye for composition, and above all, an intense study of what reality looks like. Study everything you see. Don’t just ‘look’ at it, but look at each part of it. Where does the light fall, are different parts of it discoloured, and if so, why? Does it have dust, fingerprints, grease, etc. on it, and if so, why and where?
Finally, remember that ultimately, it is only what is seen that matters. If you use a photo to create an image, it doesn’t matter, - it’s not cheating. Don’t model details that will never be seen, when a texture would do the same job.
Oh, and don’t try to do everything at once. Draw it on paper, take your time. Throw it away and start again. Have fun learning to do it better. The journey is the fun.