The main lesson I learned was probably to start thinking “in hardware” and not software. Like you design something and it fits on paper but in reality, it might not be ideal. For example, my diode placement is very close to the hotswapsocket (i fixed that for rev 1.1). On paper it war fitting, but its kinda hard to solder when you need room for your solder iron in between - this is something kicad won’t tell you.