Trade up value is largely determined by a chart established by Jimmy Johnson when he was with the Cowboys in the 1990s. Before the Cowboys fleeced the Vikings for running back Herschel Walker, teams did not put as much a premium on draft picks.
After the Cowboys got the chance to re-invent their entire roster, and went on to win three Super Bowls with only a middle-level roster salary, teams began paying more attention to their draft picks.
Here is Johnson's Trade Value Chart and the points given for each pick in the upcoming draft.
Taken from Pro Football Reference