I wish I were creative
All you need to do is imagine a star ship and how you want it to look then start building it. Experiment with different ship parts, using the ship designer to make your own unique custom ships is like playing rock, paper and scissors. It's really hit and miss with ship parts, use what looks best to get the result of ship you imagined for the race your playing, discard parts that do not give you what you want. Don't be in a hurry to build, take your time. Save unfinished designs to work on or tweak later, Patience is the key here.
I agree with Rand. Great design requires experimentation and patience.
Here's my two cents... I find it helpful to start with an overall simple shape--some of the most iconic ship designs use one basic shape for their silhouette. Try using multiple parts to make something triangular, or circular, or square--once you've got a basic shape, you can always add other shapes to the design.
For example, those awesome star trek designs Rand is posting are really comprised of one basic shape implemented a couple ways--a saucer (which is really just a flat cylinder) and two nacelles (which are long, skinny cylinders). Of course, he's added some beautiful details as well, but like he said, that just takes some playing around and some patience.