1) Do a visual inspection:
- Check solder connection
- Check component orientation
- Check correct components mounted (especially the power regulators)
2) Slowly apply power.
- Keep the current limit low.
- Gently increase voltage in steps.
- Check voltage regulator(s) output(s). Check from low voltage to higher. I.e. 3.3V regulator, pause at 3.5V, check output (<= 3.3V).
- Keep an eye on current consumption. Increase if needed.
3) Check for components getting hot.
4) Optional: watch this video
https://www.youtube.com/watch?v=fEQyW0qQFjk (First power of device!)
5) Program software
6) Check functionality