We often make much of the complexity of analyzing and building an NFL roster and forecasting how the team will do. I will propose a very simple way of forecasting success and it is totally based on looking at the quality of first round draft picks. You can either call it simplistic and stupid or call it brilliantly elegant in its simplicity. Look at the first round draft choices for a team for a few years in a row and the quality of those draft choices will be strong indicators of success of the team for the succeeding 5 of 6 years. It is not a perfect system of course, because it ignores 2nd round picks, FAs, etc, but you'd be surprised how well it works. My contention is that sustained success (i.e. over a 5-6 year period) is only built through the draft. And while you occasionally get a star like Tom Brady in the 6th round or a pro bowler like Justin Tuck in the 4th, best players usually come in the first round.
To draft successfully in that first round, you need to find a player that is a solid starter for your team, once in a while find a star and avoid minor contributors and complete busts. Take a look at the Giants draft choices over the last 30 years or so with the success/lack of success in the several years following those drafts and I think I can prove my case:
In the 1970's Giants drafts were simply awful, drafting nine players from 1970-1978 only 3 of which were legitmate NFL caliber players. Of the 3, only one was a capable starter, Brad Van Pelt who was a very strong player. Consequently, according to my theory, Giants were awful in the '70s. Things turned around in 1979. Beginning in 1979 through 1984, Giants drafted 3 starts in Simms, Taylor and Banks. Of the other 3 players they drafted, only one was a washout, while the other 2, Mark Haynes and Terry Kinard were solid starters. Giants had sustained success from 1985 through 1990 winning their first two Super Bowls and constantly being in contention following this six year period of good drafting.
Beginning in 1985, the drafting started to decline, with Giants getting a few decent players in Mark Ingram, Eric Moore and Rodney Hampton, but 3 poor picks in Brian Williams, Eric Dorsey and George Adams. In the years following the 1990 Super Bowl the team was very up and down. Then in 1991, the first round draft choices declined greatly again. In the 13 years from 1991 through 2003, the Giants had six complete busts: Jarrod Bunch, Derek Brown, Dave Brown, Thomas Lewis, Cedric Jones, Ty Wheatley, Ron Dayne and William Joseph. They had a few decent players in Ike Hilliard, Shaun Williams, Will Allen and Luke Pettigout, with one player that could have been great and never quite reached his potential in Jeremy Shockey. Giants made it to the Super Bowl in 2000 and had some decent years here and there sprinkled in, largely because of later round draft choices (Strahan, Barber, Armstead, Toomer) and a few good FA pickups (Kerry Collins, OL-men right before 2000). But that does not lead to sustained success; it was good season one year, followed by an awful one the next year, culminating with a 4-12 record in 2003 and the departure of the coach.
Now let's look at what I'll call the "Eli era", where it seems like every year, Giants are getting at worst solid starters and are hitting home runs with some real stars. Since 2004, the draft picks have been: Eli, Webster (2nd round, but first pick for Giants that year because of Eli trade the year before), Kiwanuka, Ross, Phillips, Nicks, JPP, Amukamara. We don't know how Amukamara will turn out, though he is starting to show some talent. But of the 7 picks between 2004 - 2010, Giants had 3 superstars in Eli, Nicks and JPP; 3 superior players in Webster, Kiwanuka and Phillips; and one solid starter in Aaron Ross. Of course, Giants have had two more titles since this 2004 drafting period began and their worst record was 8-8. By my theory, that success was predictable and it bodes well for the Giants fortunes for the next several years.