1.) Have a focus. Set it up so the scene draws you in to a main structure that you spent a long time making. A great example of this would be the gunner in Prometheus being the focal point and the organic textures around him being the environment. Another example could be a destroyed street in the middle east somewhere…
In general, modular modeling makes for very boring environments. You have to expand beyond that to create something interesting. I'm not saying don't do modular, I'm saying thats not the answer to your question. what makes an environment interesting: tell a story. tell several stories. anything that you can convey to the…