#1 Reunite The Shield
Isn't this a bit obvious? When WWE was going for the Shield reunion in December 2017, those were the few times Roman actually got cheered. Even though Ambrose's injury scuppered the reunion, it was the right step in rebuilding Roman in the eyes of the fans. If WWE can play off that nostalgia, and build Roman from there, it could possibly make him the mega-star that WWE has been trying to make him.
The post SummerSlam lull is the perfect time for this to happen, as Ambrose would have returned. Teaming them up and have them be a stable against the foil of say Ziggler and McIntyre, or a new authority stable with the likes of Owens and Corbin would be a perfect way to book them. Have this culminate at Survivor Series against a team from SmackDown like Sanity or New Day, and then use Roman as the bet he has the potential to be. He needs to reconnect with the fans, and this is probably the best way to do so.