he first is health. Football is a sport of attrition. Those teams that have balanced rosters (using all 45-53 men) are best able to interchange players when injuries occur. Coaches always say "injuries are never an excuse". Fine, but they are the reason teams succeed and fail.
The second thing that matters, and this trumps everything else, you MUST have a franchise QB. Period. Case closed. Sure you can be a "one hit wonder" and win a SB with an average QB (1987/1991 Redskins, 2000 Ravens, 2002 Bucs), but to have any type of sustained success year after year, you need a franchise QB. It's no accident that (not in any particular order) Tom Brady, Peyton Manning, Aaron Rodgers, Russell Wilson, Big Ben, Joe Flacco, Drew Brees, Andrew Luck, Eli Manning, have their teams competing for playoff spots on a yearly basis. It's rare that those teams are going to be mitigated disasters and finish 5-11. With a franchise QB you always have a chance to get into the postseason (which in the NFL just making the playoffs is an accomplishment). It's why teams are willing to break the bank to keep their QB's once they deem them franchise worthy.
Look at the history of football. I guarantee that any team with a 7-10 year period of sustained success (making the playoffs more often than not) have a franchise type QB at the helm. Having one masks a lot of the other flaws on your team.
So its all well and good that the Dolphins signed Ndamukong Suh to a massive deal or that Byron Maxwell signed a massive contract with the Eagles. IF Ryan Tannehill or Sam Bradford don't show any maturation, both the Dolphins and Eagles are sitting home for the playoffs.