Genie+ is the old paper fastpass system moved into an app. You can make your first reservation at 7 am, then once you use that one you can book the next one. Repeat until all the reservation times are gone for the day. So your strategy reverts to the old fastpass system when it comes to which ride you choose first.
Similar to the old system, if your next reservation is more than 2 hours away, you can book another pass before you use the one you already have. If you try to make a second reservation too early, the app will tell you what time you can make the next one at, which is very convenient.
Unlike the old Fastpass system, each park has 1 or 2 rides not included in Genie+. These are the individual
lightning lane attractions, and you buy a one time pass for them. These can be convenient because rather than getting the next available time, you can choose when your reservation is. This way it won't interfere with any dining reservations. I like to book them for the afternoon, when lines on everything else are at their longest. On-property guests get a bit of an advantage with the individual ride purchases. They can buy passes starting at 7 am, while off-site have to wait until park open.