I am always fascinated with how head coaches and GMs determine the 53 man roster. Living within 2 miles of Gillette Stadium, I have long studied the way Bill Belichick and the Patriots make their roster decisions. One of the reasons why the Patriots are a championship caliber team year after year (other than QB Tom Brady) is that they always factor the future into their drafts and roster decisions.
The way to start the process is to write down the number of current players who are in the last year of their contracts in order to determine how many of them will likely be playing somewhere else next season.