So one of my all time favorite things to draw, design, and pretend to have, are space ships. I've learned a lot over the years and more recently, I've been applying various techniques and process into my personal work. The process used for these was pretty straight forward : "Sketch" in 3D program, then draw over the outcome. For each of these I had an idea in my head of what I wanted before I started , so i didn't doodle around forever with the infinite possibilities of 3D.
This one was more of a grounded approach, maybe some kind of earth defense ship. I spent a little more time working out the forms, also it had rocket pods at one point.
Here is a bit of work on the lines. Mirrored, and now lacking its rocket pods.
So far my experience has been fairly fluid. Fortunately I know most of the basics of Maya, so I can maneuver around and create pretty quickly (3D animation minor finally put to use) . I highly recommend picking up any 3D; sketchup to maya, to help block things in. I'd say for these it helped me get the perspective and forms down quickly, so i could move right into details etc. Frankly, its building with Lego bricks, except you're making each brick as you go.