Answer:
Each teams plays
2 games against each division rival = 6 games
1 game against each team in another division but the same conference = 4 games
1 game against each team in another division that is in the opposite conference = 4 games
1 game against the teams that came in the same place as you the previous season in the same conference (ex. 2nd place in AFC East vs. 2nd place in AFC South) = 2 games
Look at the Jets schedule this season (I'm a jets fan) - they played their division rivals twice, played the entire AFC North, the entire NFC North and since they placed 2nd in their division last season, they played the Broncos and the Texans who each came in second place in their divisions as well.
Each year it a rotation- so next season the Jets will play the AFC West and NFC East plus the team that comes in second place in the AFC North and AFC South