Each week you are scheduled to play someone else in the league. You pick all the games against the spread. You must double-down on one game, making it worth two wins or two losses. Total points for the MNF game is the tiebreaker.
The person with the better record gets a win, the other person gets a loss. Pretty simple.
As the season moves on a person's overall picks record is the tiebreaker for seeding purposes.
John 8-4 59-40
Jeff 8-4 57-42
John has a better overall pick record, so he is higher in the standings.
Week 17 of the regular season is the first week of the playoffs. Your league commissioner must pick the 5 most competitive (aka important) games to be your "playoff" games. In my league of 26 teams, the top 12 teams make the playoffs with seeds 1-4 getting a bye. Seeds 5-8 have have "home field advantage" against 9-12, meaning if a matchup ends in a tie, the higher seed advances. This advantage lasts for three rounds, until just 2 players are left. The conference title games and the Super Bowl count as one "week" with the final 2 players picking all three of those games, but using their double down just once, meaning they can use it on a conference title game or save it for the Super Bowl. We never let the two finalists know where they stand after the conference title games so their SB pick isn't swayed by that knowledge.
For fun, you can also incorporate a suicide pool into your league as well as weekly best record pool, with the winner being whoever has the best picks record in each week. Like a skins game in golf, there can be carryovers. If John and Jeff both have the best record at 12-4 in week one, it carries over to the next week with everyone eligible to claim the doubled prize.
That's it. It's lots of fun and a nice alternative for non-fantasy and fantasy players alike.