I've found that the new jungle isn't anywhere near as bad as people make it seem. And I've been playing as Trundle, who is a strong jungler, but not god tier by any stretch. The key is to constantly look at what is happening in the lanes, ward appropriately, and gank early.

Just pick champions that you enjoy, practice your routes in Co-op vs AI, learn your timings, then play normal Draft modes to further practice. There are different roles that you will need to learn as a jungler, like counter jungling, baby sitting lanes and knowing who to gank, and when. Most importantly, communicate with your team, if your solo top has fed their WuKong 3 times in the opening few minutes and are crying for help, know that a gank is a bad choice, and a lane change would work better (and after the 2nd death, they should probably be looking to change lanes anyway).

Enjoy jungling, when it goes right, you will win your team games, if it doesn't go smoothly, then get used to Solo Que team mates blaming you, because apparently it is always the Junglers fault if you loose.

Dont go fiddle dont go work with new jungle.
You'll need a aggresive jungle to influence lanes in the current jungle think rammus, lee sin, singed.

cough twitch cough

I've been jungling for over a year and in 1900 elo games these champs win games and are able to snowball.

Udyr, Leesin and skarner all the junglers that you'll ever need. Unless riot nerfs irelia then we'll have to jungle karthus

Nocturne is very solid in the jungle and has very powerful ganks, even pre 6, considering you land his q which isn't TOO difficult. Lee Sin is a bit more difficult considering his q doesn't go through minons, although it's a guaranteed gap closer if it lands. Warwick is meh in this new jungle simply because he HAS no gap closer. He relies too heavily on red buff. Skarner doesn't need it with his q. My suggestion: Start Udyr. He's easier than noc or lee.

Jungle GP is the easiest. Parrley slow, Ult slow. You can AFK jungling and global ult if you want.

The strongest: Udyr, Skarner, Lee Sin, Trundle and Maokai. They pretty much out jungle everyone. Beside Skarner, they are all a bit weird and need some getting use to.

Shaco:

Pros: Ganking is extremely powerful if your teammates listen when you tell them to harrass and not push that hard. Can escape almost any gank at level 4+. Can help teammates escape.

Cons: If you die at red buff, you lose a lot of time to regain blue + red and level. ( not likely ) When you use your ultimate and you hold a buff, the fake shaco doesn't have the buffs with it.

Fiddlesticks:

Pros: Jungles very well if you have drain at at least 1 second cooldown reduction. Ganking is very powerful when you crowstorm/ flash. Can take out many people in team fights.

Cons: Jungling is somewhat slow as in getting to the monster. Without blue, you have to recall many times (early game). If you get ganked while jungling, you're done. unless you have flash (recommended)

Warwick:

Pros: Great jungler. Once you have ultimate and team cooperates, people will get very annoyed and you get kills.

Cons: Hard to escape team ganks. People usually stay back when opponent as a warwick ( I know i do ).

Nocturne: Never tried :/
Lee sin: Never tried :/
Skarner: Never tried :/

I've been working with Amumu as a jungler. His Q and ult are great ganking tools. You just have to be able to land the Q.

Don't play WW as jungler, he's not as good as before. I play him as bottom duo or solo top.

Warwick is a great jungler

Nope. Terrible in the new jungle. New jungle is a AOE jungle. WW clears it a bit too slow compare to other top tier junglers now.

Can't even gank before lvl 6. That couple with slow clearing (meaning slower lvling), you get the picture.