Honestly. Stop completely with doing story missions, 9 Tails, and the Kakashi daily missions as those give you a lot of exp.

Just spend everything into getting power items. Continue to reset ninja exam and get higher levels. If a ninja you use frequently has elite instances or can be optained with ninja points, 5 star them. Get training potions, refines, cave keys, just every single power option. Your choice if you are willing to wait for rebates or because you're low on power, to use them now.