Everyone has good insight so far - I would add that this video[1] from CGP Grey comes to mind about picking a theme for the year ahead. It's easy to get bogged down in the details but I try to follow a heuristic of taking action is infinitely better than sitting down and endlessly ruminating about it (of course easier said than done).
[1]: https://www.youtube.com/watch?v=NVGuFdX5guE