Hmm, here's a few pointers:
- Add different hull materials so it's not completely made of one material (with hull, throw in some standard and advanced armor to texturize).
- Try different hull coloring on some areas (adds detail, due to not all of he hull being the same color, also, having a color scheme helps).
- Add surface greeblies, windows and vents (the reference pictures should give you some ideas on what kind of stuff you could add and where).
- Experiment, tinker and try out stuff to see what works with the build.