Passed JNCIA 102 this month. For my studying I used the official JNCIA Study Guide, old cbt nuggets by Michael Shannon (he is perfect unlike more recent Jncia cbt nuggets).
For practicing I used that old olive VM + vSRX inside Eve-ng and sometimes GNS3.
I would add that 5 hour long Juniper Network Fundamentals course.
It was an easy exam, I'm now studying for my ccna i will attempt the exam in June.
Cool deal. We were told to buy some $35 software that's like Packet Tracer, but I'll look into possibly checking out the GNS3 option.
I should probably brush up on the fundamental stuff and factoidal information (what kind of routing protocol is OSPF, BGP, etc).
I've done some slight work on Juniper gear before at my job at an MSP, but nothing crazy.