From NFL.com

Two Clubs, Non-Division

Head-to-head, if applicable.
Best won-lost-tied percentage in games played within the conference.
Best won-lost-tied percentage in common games, minimum of four.
Strength of victory.
Strength of schedule.
Best combined ranking among conference teams in points scored and points allowed.
Best combined ranking among all teams in points scored and points allowed.
Best net points in conference games.
Best net points in all games.
Best net touchdowns in all games.
Coin toss.