The 24-year-old lost weight and adopted a healthier diet, but Fournette said his main focus was straightening out his personal life.
"I just tried to focus on my personal life - getting the bad people out of my life, focusing on myself so I wouldn't have to worry about no problems coming into the season or even coming to camp," Fournette said on SiriusXM NFL Radio.
Fournette has said he's looking for a "clean start" after an admittedly "bad year" in 2018.
He got ejected and then suspended after throwing punches with Shaq Lawson of the Buffalo Bills in Week 12, and was disciplined and criticized by Jaguars executive Tom Coughlin for his behavior on the bench in a late-season game. In April of this year, he was arrested for driving with a suspended license.
Fournette has also struggled to stay on the field due to injuries. He played in eight games last season and averaged 3.3 yards per carry. But he expects better in his third season.
"I know football's going to take care of itself. I put my mind into working hard every day, do what I have to do," Fournette said. "But it's really the personal things, just trying to be in a better place."