How to learn a new role when playing at a higher level?

Hello there, I am a summoner that is currently ranked gold V and is always looking to get better.

In keeping with that motto, I'm wondering how the hell you get better at a role that you don't know very well when playing at this level? Namely, I would like to learn jungle, but every time I play, no matter how well I do early, i always end up behind later on in the game. Not just behind the enemy team, but namely the enemy jungler.

I don't know how to keep up in farm, or for that matter how to become relevant again in game if I fall behind early.

Can someone (preferrably higher level) give me some advice, or might even coach me over skype or in a game on how they jungle? Any comments would be most appreciated, thanks!