I took as passed the J0-102 JNCIA-Junos exam this morning on my first attempt. My employer pays for a Pluralsight subscription and I signed up for a month of CBTNuggets to take their course on the exam as well. CBTNuggets is expensive but they have a free week to all new subscribers.
While I can't go into specifics due to the NDA, my first tip is to take a look at what Juniper says is covered and make sure you are comfortable with the material covered as the questions can come from any of the areas.
My second tip is to get hands-on experience with Junos. This is essential to make the exam easier. Used devices are readily available and affordable online and having a device to actually work on would go a long way in helping someone pass the exam.
This exam is not necessarily a difficult exam but if one doesn't have the theory coupled with hands-on expereince with the Junos OS, it will become much more challenging.