I would recommend getting Genie+ on your first Magic Kingdom day. It's the park that needs it the most, it's the easiest way to "practice" with it, and it's the park where you can still get some value out of it even if you're bad at it. It really does take some practice to get good at it.
The risk of doing all the parks without it first is that you say to yourself "oh we'll get to that on Genie+ day." Versus if you do your Genie+ days first, you can try to do as much as possible and be super efficient the first time through the parks, and then if you do a second day without Genie+, you know what you've already gotten to so you can be much more relaxed and deliberate.