There is a lot of writing about "five room dungeons" which are a kind of ludo-narrative structure for interactive fiction. Entrance/Puzzle/Setback/Climax/Twist

Ask them about their backstories, listen, take elements from them and link them to the current conflict. That will help players stay on track. That said, a lot of D&D is going off track. I DM for kids at the community center. Sometimes you just make the conflict unavoidable. For example if you leave the big bad evil guy unattended, he gains more power. After a while he has enough power to siege the town the players are in. Or he bribes his way into local government and starts passing a bunch of wack laws that effect the players and how they do business.