Jungling is sort of like playing the AD carry in the sense that you can't get a simple step by step guide to doing it.
I would recommend playing normals by yourself using a jungler you're comfortable with, or warwick or fiddlesticks. Learn routes and figure out your ganking patterns. When you feel confident, move on to playing with a couple of friends to get well coordinated ganks. And try champions you don't usually jungle with. It's important to be able to play other characters based on the respective team comps.
More than anything, interactions with lanes as the jungler are about being opportunistic. Don't be overly cautious. Farm lanes when champs go back. Steal random camps (Having map awareness helps a lot for this)