Once you've made a reservation, when you are 60 days away from your first day, you can start making FastPass+ reservations online: Walt Disney World FastPass+.
This is also where your "top list" comes in handy, so you can pick the things that matter most to you, which include character visits which you can get a FP+ for. Also, general tip for FP+: if you can get to the parks when they open (you should!), then avoid making FP+ reservations before 1pm. Ride lines are short up until about noon or 1pm, anyway, so save FP+ for 1pm —7pm which are always ride peak hours. — Quora user Ian McCullough