Here’s the path I use for leveling alts:
1. Jade Forest to 86. If DPS sit in queue for the 2 lower level dungeons while I quest. If tank or heals, queue when I want to do them.
2. At 86 go to Valley, remain in queue if I haven’t completed both dungeons.
3. At 87 get the quest in Halfhill to go to Kun-lai. Do the quests on the Veiled Stair to get there. Quest through Kun-lai until completion [I love this zone]. Should get me well into 88 but perhaps to 89 depending on how many instances I do. Queue once again for the two new instances available at 87.
4. Once Kun-lai is done or at 89, hit Dread Wastes till 90.
I have varied on this once, finishing Jade forest to completion and then hitting Krasarang, but I typically like the familiar path to do it more expediently.