Jungling is probably one of the more complex roles in LoL, imo. You have to balance farm with ganks and helping the lanes whether it be by ganking or alleviating the frustration of one of your lanes getting zoned out of CS while also dealing with the possibility of counter Jungling and dragon/baron.
In a situation like this it is not only your fault. Warding is the responsibility of the entire team. I would advise you watch your lanes and remind them to always keep their wards up. The game gives us two free wards now and wards are only 75 gold. Every player should be buying a ward on their backs until they have full item slots.
In addition, learn champion match ups and gank lanes where your team is at a disadvantage. For example if I have a Zed on my team and I know he is rushing BotRK for his combo I will definitely gank mid pre level 6 to ensure that he can farm and rush his item easier. Nasus in top is always a champion I want to gank and even if a kill is not secured because he cannot be allowed to farm comfortably.
Offer the buff that you do not need to someone who can make better use of it. For example, I typically jungle as AD for personal preference so my blue buff is always offered to an AP based champion.
And finally, back to my first point. Wards, wards and you guessed it.. wards. Kill scuttler as often as possible as the free ward and speed boost do not only offer vision but speed as well. Keep areas of the map that are seeing heavy traffic warded at all times. I always like to keep vision on drag and when drag is down drop a ward on it around 1:30 on the respawn timer.
Cases where the enemy jungler snowballs can be difficult to handle especially when one lane is continually the victim and due to so many junglers having the ability to carry. I'm talking about Sated Master Yis with teams full of CC or some of those insanely good Rengars or Lee Sins running around the Rift like its nothing. Choose your jungler wisely, you can make or break a good team composition with your choice.
