Bill Polian's do's and don'ts for NFL free agency:

It is a rare thing to be able to find good value in NFL free agency. The main reason for this is that teams almost always try to keep their top players on their rosters, so if a guy gets to free agency there's a good chance it's because his team has made the determination that his future value will not equal the amount of money required to keep him.

And given that this player's team knows him better than any other in the league, that can be a concern for teams considering signing the player before the evaluation process even begins.

However, that doesn't mean that there are never values to be had (either because a team has too many good players to keep all of them, or other circumstances), or that even if a team has to overpay a little bit there aren't quality players available who are capable of helping it win.

At right you will find my 14 tips for approaching free agency, which I expanded upon in an article last year. Below you will find my grades for this year's free-agent class, with analysis included for every player who earned a B-minus grade or better. I explain my grading process throughout, but in short, A players are consistent difference-makers and B players are starters who can help their teams win.

Here is my Big Board of the best available free agents for the 2015 class.

(Note: Players are listed alphabetically within each grade, and players who were franchise-tagged or transition-tagged are included to show their relative place within the marketplace.)

A-plus

Players graded in the A range are defined as those whose talent, physical gifts, durability and production allow them to win their one-on-one battles with regularity and make a difference in winning each week. By definition, there are three-down players.

Ndamukong Suh, DT, Detroit Lions

Simply put, Suh is the best defensive tackle in the NFL. If not double-teamed, he will win virtually every time.