1) Use the minimum number of sizes of drill holes.
2) Keep audio traces as far away from digital traces.
3) Put as much text information on the board layout (circuit layer) as possible.
4) Verify dimensions of the circuit board so it will mate with sockets or card holders.
5) Identify pin 1 of all chips.
6) Try keeping all IC's in the same direction.
7) Use a star ground for low ground loops. Consult engineering if separate grounds are required.
8) Use relief's for joining large pads to small traces.
9) Identify component side, assembly side, silk side, layers.
10) Place signature and date codes.
11) Place part number of board on board layout (circuit layer).
12) Make power and ground traces as wide as possible. All traces should be was wide as possible.
These are some of the checks I use when laying out circuit boards. I will add to this list regularly. Your input would be appreciated too! Contact me. Thanks!