I have learned a lot about 3d design and printing from the various models I have created, and am trying to incorporate enhancements to my new designs. I also plan to go back and add these same improvements to my existing models as I have time.
First, I realize that mirrors are a fairly critical detail for my trucks, and while my very first finished models had no mirrors, I began adding my own custom mirrors to my recently finished trucks. I simply use brass wire bent to the appropriate shape, inserted into a #80 hole that I drilled into the cab. I am amazed at how 3d printers can print a very small hole into a model like my truck rims, and I came to the conclusion that I could simply design my trucks with the hole already printed, ready to accept a piece of wire. This way, I can avoid damage to the model from my drill, or trying to hold the model while getting the hole started. The biggest benefit is having precision location every time. On a couple of my models such as the Pete 386, I designed a mirror assembly, and added these details to the wheel and tire sprue. I also added the appropriately located hole in the cab to accept the mirror.
Second, I recently uploaded a file of dual wheels and put them into a square pattern rather than a long straight line. I have had mixed results from Shapeways, as they like to print these long lines at various orientations, since they likely find extra spaces in the print tray for these long strings around other models. The wheels that get printed flat with the rim facing up are usually a very clean print. If they are printed on their side, they have texture. Since I changed the pattern, I have had great feedback on print results. So, now my wheel sprue pattern is rectangular, to promote flat print orientation by Shapeways.
Third, I beefed up my front axles, and added a shoulder that allows the front wheel to slide to the accurate location. Up to this point, I have had to trim the axle and eyeball the spacing of the front wheels. I now realize that I was making things much harder for myself in the assembly stage.
I know there are probably many other things that I will discover in future models, but wanted to share what I am beginning to incorporate into my designs now. As always, I am open to feedback and suggestions on how I can make these better.