dont bother with jungle, it is complete **** now, you will be behind on money and exp unless you jump into lane for a couple lvls
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.