Poppy jungle is very good. She has great survivability and great clear time with her Q.
The trick to Poppy is to not go for kills, but to go for utility. Build her tanky and learn to get her combo going by mastering her E. Position and slamming an enemy into the wall is key to getting off her big damage. E into wall, then while they are stun hit them with Q, followed by W to stop them from dashing away.
Another good CC Combo is E into uncharged R into Q into W. Not charging her ult fully will allow Poppy to knock enemies UP rather then back to their base.
Her ult is a game changer. One good ult will turn the tide of a team fight. Knowing when and who to ult though is key. If you find yourself losing team fights your going to want to remove the heavy damage dealer from the enemy team with your R, knocking them away and causing the enemy team to lose a good portion of their team fight damage will change the outcome of a team fight.
Learn to peel. Poppy is great at it. Q slow. E stun, W stops dashes. protect those who are most important to the team, Poppy is not a good initiator unless she catches someone in the jungle and E's them into a wall. Let them initiate or if your team has a powerful initiator, let them do it.
Poppy really is all about tank and utility, her damage comes from her Q and when pulled off its quite alot, let your build cater to your team.
Is your team very tanky but lacking damage?
are right for you.
If your team already has quite a bit of damage but needs a tank.
are right for you.
One last tip, Poppy befits amazingly from cool down, Spirit visage is great for that reason but some CD runes and masteries never hurt.