Here is a great reference of a spaceship done right. Notice the details that give the ship a sense of scale, the running lights, the spotlights, the nurnie shapes. The shot with pool window tells us something about the size, we know how big pools are. The planet looks good and they have a lot of the blue atmosphere at the edge of the planet. The rings are weirdly placed but look good. The pod thing has great heat effects, and that's good compositing.
You model out basic shapes to get the overall shape of the spaceship, The Death star was a sphere, the star destroyer was a wedge, the x-wing was an x, you get the idea. Fighters are sleek and narrow, In Guardian's of the Galaxy, the nova core fighters were star shaped. Cruisers in Legend of the Galactic Hero's had different shapes, some were stretched out cubes mostly. The flagship was an oblong rounded wedge design. The thing to remember is that the silhouette is most important. That's why an x-wing is so memorable. The tie fighter the shape is simple and memorable. You can add on as many details as you want for close ups, but from a medium to long shot, the silhouette is most important.
After you have the shape, you can add in details, like greeblies, and now in blender using micro displacement.
He goes over shading and tips to make general space stuff, a sun, a blaster, a planet. These are as he says great to get previz ideas off the ground.
Uses single sun light, and shows some compositing nodes to get a nice subtle Glare. Great tip for your space renders.
Mr. Bailey makes a pretty good spacestation, and he blocks out the shape first and then adds the details. One of the best things he does is turn on snapping, and snaps his greeblies to the station. Using the set origin to cursor helps before you duplicate your greeblies. Set the cursor to the bottom of the greeblie in the center.
Chip Walters makes a great spaceship using several techniques in BLender. The microdisplacement really helps in adding the details.