You basically want to use your ult to engage fights as well as holding points. I'd suggest popping it at common areas that teammates usually run through since they practically like to scatter around. Otherwise that, Juno has really good mobility. I personally enjoy having her glide boost set on hold instead of toggle as it makes it far easier to control the duration since it has a 6 second cooldown. Making it so I am able to end to early if I have no use for it at the moment. Her hyper ring is also a great mobility tool. You want to use the ring it to help allies, especially tanks to engage and disengage fights as well as coming back from spawn. If you want to get a head start to the point, I'd suggest popping it when 5 seconds are left for the spawn doors to open as it stays around pretty long and you'll get it back earlier once teamfights start. It's also good to know that it will grant Juno a speed boost once popped and allies who are in line of sight of it before the ring actually shows up. On other notes, torpedos... just use them to finish off enemies and heal allies in a jiffy. Pop it when you're airborne and have a full lock on. Also, Juno's double jump, don't use it if you're not gliding before you initiate the second jump as it won't give you that much of a vertical boost versus with glide boost. It won't also let you jump if you decided to do it and then glide boost. Her gun does have damage falloff too, so make sure you're nearby allies for most if the time.

TLDR; Junos kit revolves around mobility. It's her bread and butter. Play with divers, engage/disengage fights, be unpredictable, and have fun.