This PCB design checklist contains things you should check before you send a PCB off to manufacture. It includes generally good ideas and some lessons learned the hard way! Feel free to update as experience is gained.

1. Schematic Checks
   1. Check component values (including tolerances and power ratings)
   2. Check component pinouts (check against the footprint too!)
   3. Check over any complicated or novel sections of the schematic, especially e.g. high power and RF
   4. Check pin allocations on a microcontroller are compatible with required peripherals
   5. Check any serial lines have RX/TX swapped where required
   6. ESD diodes on all world-facing connectors
   7. Check all parts have order codes for the correct item
   8. Check app notes and datasheets for novel parts for hints on decoupling, layout, app circuits, etc
   9. LED indicators (status, power, etc)
   10. Use reasonably large LED resistors - don't need to blind anyone with indicators
   11. Don't mix up global and local/hierarchical net labels
   12. Check label directions are appropriate (inputs/outputs/bidi/etc)
   13. Run ERC: no errors or warnings
2. PCB Checks
   1. Decoupling capacitors all close to IC power pins, with smallest values closest to the pins
   2. Power nets as simple and tree-like as possible. Avoid loops
   3. Ground pours should have a bit more clearance than the minimum
   4. Stitch ground planes together well if using more than one
   5. Crystal traces as short and symmetrical as possible
   6. ESD diodes as close to connector pins as possible
   7. Check component footprints against datasheet for new footprints
   8. Double check pinouts on the PCB against the datasheet
   9. Ensure sufficient mounting holes are present, with enough clearance for bolt heads
   10. If the PCB has to fit in a specific geometry, check board dimensions and connector placements
   11. Silkscreen:
       1. Date, revision, name
       2. Pin 1 indicators
       3. Power and other connector pin labels
       4. Clearly mark polarity and functionality for connectors
       5. LED labels
       6. Orientation labels
   12. Check datasheets for specific PCB layout advice
       1. No copper underneath magnetometers
       2. GPS receiver ground planes on both layers
   13. Add test points to nets of interest
   14. Print out a 1:1 copy and inspect visually for anything that stands out
   15. Check over mask and stencil settings: avoid too much mask or paste
   16. Check positions where they're important, e.g. board mounted connectors, outline shape, location of mounting holes
   17. Round off PCB corners
   18. Check power traces are as thick as practical and ground planes as complete as possible
   19. Run DRC: no errors or warnings