Why poppy? Simple! She is the best anti-meta champion of season 7.
Her W defends her and her squishy teammates against the new reworked assassins, almost every single one of them. And i'm not just saying this because i absolutely love playing poppy but she is in my opinion one of the more strong junglers of this season.

~ Cinderhulk: You want to get this first because it highly increases your clear times in the jungle as well as it makes you almost unkillable.

~ Boots Of Swiftness: You want to get boots of swiftness because you become almost inescapable for champions without dashes or movement speed increasing abilities.

~ Titanic Hydra: This procs on your passive as well, Try pressing you're titanic hydra while you're shield is flying towards you're target. this will still trigger the bonus damage of you're titanic hydra even if u activated it mid air.

~ Start the game at blue and continue to wolves and then red, this should make u hit level 3 which means you're full hp if u did it properly. now u have double buffs and all skills.

~ From there u can decide to gank lanes or keep farming, After you got you're cinderhulk i prefer to clear the red side because the small raptors and golems die really fast cinderhulk combined with you're Q.

( Warning: DO NOT USE SMITE ON FIRST BLUE! )

Try picking off low mobility lanes once u hit level 3 after red since you're full hp u can easily sustain the enemies damage and cc them long enough to kill them, if there are no low mobility lanes or all lanes are push do not be afraid to go counter jungling, poppy has a lot of early tank stats combined with based hp damage makes it easy for u to kill squishy junglers.

You're build on poppy is solid for the first 3 items: Titanic, Cinderhulk and Swiftness boots.
After those 3 items it becomes sorta situational since u can just build more magic resist if there high on AP and armor if there high on AD

Pros:
+Strong Early Presence
+Fast Jungle Clear
+Shield Provides Good Jungle Sustain
+Powerspike at level 7/8 With Cinderhulk and Boots
+Strong CC
+High Base Health and Defense Stats
+High Base Damage
+Full Tank Almost 1shots adc's
+R makes teamfight 3 or 4 V 5 when used properly

Cons:
-Weak versus kiting
-Ultimate is hard to learn