What are the top "traps for young players" in basic PCB design?

[Cerebus]

If you have enough layers, a ground plane will take away an enormous amount of pain in anything fast, sensitive or noisy. If you don't have enough layers use polygon pours for ground wherever you can.

[kendalll]

Home etching a pcb seems like a waste of time and effort when there's options that are pretty affordable and reasonably good quality. https://oshpark.com/pricing

I mean unless the process of doing it at home is really fun for you...