Need Jungler advice.

So I started jungling Vi when I first began playing pvp, and I used to be really good at it. Unfortunately while trying to branch out into new roles, I stopped playing jungle a lot and began to focus more on mid and support. Due to this I've gotten pretty rusty at Jungle. The biggest issue I have is knowing when it's a good time to engage, and how to engage. With Vi I usually always engaged with my Q or Ult, but now I want to start taking jungle more seriously with champs like Shyvanna (Who I used to play top lane with, big adjustment), or potentially a Jungle Ekko .

Any recommendations or advice would be greatly appreciated, thanks!