PCB layout is tough. Laying out a PCB isn’t in itself too hard once you learn how the tools work, but high-speed (10MHz+) introduces a virtual mine field of potential issues that you may not be aware of until it’s too late. While experience is the best teacher, Analog Devices has a great application note explaining some of the key pitfalls to avoid when dealing with high speed designs (which is basically anything today): A Practical Guide to High-Speed Printed-Circuit-Board Layout. Some of it is a bit heady, but not more than it needs to be, and it really does lay out a lot of key information that you may not have been aware of. Want to improve your PCB design skills? Print this out, and keep reading through it until it starts to make sense. There’s years of bench time worth of information in there.