Auto-promotion (for non-finals winners or extra promotions to fill in for bot demotions) is based on regular season record, ranked on the following order:
1. Position of finish in your conference (as a practical matter, you have to finish first in your conference to auto-promote out of d3 or higher in the US, there simply won't be enough auto-promotions to get to teams who finished 2nd in their conference)
2. Total wins
3. Point differential
From d3 to d2, there will be 4 guaranteed auto-promotions a season, plus the 16 finals winners. So the top 4 d3 conference winners by wins and PD are already guaranteed. Positions 5-20 have a chance, depending on how many people above them in the aggregated standings win their finals. Positions 21 and lower could only auto-promote if there is a bot in d1, or a bot in d2 that won't relegate through the normal relegation process.