As far as tips go, I would say that doodling and doing thumbnails really help to find interesting shapes. It's also important to try new things and experiment with shapes. Most of my ships are based on basic 3d shapes that are cobbled together. Once the basic shape is there, slap on some engine pods (Star Wars ships are the best examples of these) and then do the details. Details make a big difference and Star Wars and Battlestar ships have some great detailing. Check them out carefully and try copying their detailing initially. Also, take a look at big machinery (graders, diggers, cranes etc.) to see how they work and how their parts fit together. The main thing is to be patient and keep trying. Do it for yourself and do it for fun with no grand illusions and you should be churning great stuff out in no time. Good luck. I f you have further questions, feel free to contact me.