Although you wouldn't guess it the Vikings ball possession metrics were not horrible last year. They ended up the season about 50-50 between offense & defense. But that is somewhat shortsighted since there was an overwhelming amount of pressure on the defense to win games and put points on the board.
What really needs to improve is red zone play. Last season the Vikings were in the red zone an average of 3.1 times per game which is slightly below average. But the offense only scored points on 46% of their red zone opportunities which was third to last. A below average number of attempts and a horrible conversion rate on those attempts is a recipe for disaster.