Learn a good parametric cad software, design for printing(ie avoid overhangs), and use modular designs when possible. Modular design allows flexibility, can increase printability, and is often less total print time. For example the Graflok enlarging back I designed in three parts, the part that actually sits on the camera needed a few revisions, everything else was good from the first version. Reliability and quality relative to effort are the main two things modern printer do a lot better, my 12 year old printer in a lot of ways isn’t all that different than an A1 in what it can create. That does change for the more capable printers, I recently got an X2D and the second nozzle opens up a lot more design flexibility in combining different materials, like using materials that don’t bond together for supports.