Do you design or define PCB layouts? If so circuit board, what rules and checks do you have in place to make sure your results are... optimal? 

Over the years, I've created a PCB design checklist to keep me out of trouble. I share these nuggets with my layout person as required. Allow me to share some with you. Starting out The first thing I always say is "Do not let the tools dictate the board. Imagine how the board should be, then implement it. If it's too difficult, consider new tools. 

But still implement circuit board it." I think that's self-explanatory. Planning is the critical first step. Plan a stackup. Plan the part placement. I'm sure you can chime in with more. In my book, stackup professtional pcb prototype(pcb.hqew.net) is almost an art. There are so many dimensions to consider, and some always conflict. Reduce cost by minimizing layers, but don't go so far that it takes an extra month to lay out the board, SI suffers, or you just can't fit all those parts into the space allotted. 

You usually want to keep the layout balanced around the center of the stack. This minimizes warpage, which is a really bad thing when you have large SMT components. Try to have your board fab circuit board team selected before you start. They can answer general and DFM-related questions and help you get your controlled-impedance traces right. The fab will almost always make slight adjustments to your controlled-impedance traces to compensate for their processes. The tighter your design is, the more you'll have to concern yourself with this. 

Make sure all special requirements are spelled out, whether in documentation circuit board or as part of the schematic. These can be things like high-current nets, thermal sinks, length matching, controlled impedance... but I'm getting ahead of myself. We'll get to some of those in the high-speed area. Sometimes you can draw a schematic to hint at the required layout. A classic example is a single-point ground node. Of course, this only works if your board designer knows to look at the schematic and can understand your notations! On any design that's even approaching high-speed, I always insist on a good density of ground vias sprinkled throughout the circuit board, so that a good scope-probe ground is always available, no matter where you're probing. 

These should be circled on both sides for easy identification. Hell, they should glow in the dark. I'm a great fan of flooding – on lower-speed double-sided boards, at least. Flooding unused areas with ground (and power sometimes) is a great way to improve power quality. It can improve etch consistency and reduce coupling, and it is a circuit board good idea environmentally – there's that much less copper to be eaten away. 

A similar concept is thieving, which is often used on higher-speed multilayer boards. Here, empty areas are filled, not with a solid flood, but with a pattern of dots, a grid, or something similar. This helps maintain an even copper density over the layer, which again helps with warpage. Given the concerns I've read about floating islands on high-speed boards (leading to coupling or a resonant patch), dots are probably better than grids.