Most of these questions are answered with notes and journals in this AP, which some GMs (and players) find a bit boring. Off the top of my head:
-going to Thistletop: Tsuto's journal
-going to the Misgivings: note from ghast in the farmlands
-going to Turtleback Ferry: Xanesha's letter
-going back to Sandpoint to defend against giants: Barl Breakbones' notes
I think these are more for when you don't have anything else as a GM to steer the players in a certain direction. If your players have certain motivations, you could use other things like NPCs to steer them in a certain direction. In the Thistletop example: maybe have a guard NPC tell the PCs that they saw goblins go north-east, or sailors who saw goblin activity increase near Thistletop, or rumours of gold and treasure in that area, etc. Also, if you can somehow tie in the PCs backstory to go in a certain direction it's even better. But all of this can be a lot of work of course, so it's good to have something as simple as a note to fall back on.