I am currenty on my second FF OW J class RTW trip. My advice is to plan as far in advance as you can, I start planning months before I book . I use QF website this gives you an idea on what flights are available and on what days, times etc. I plan my itinerary around availability. QF website doesn't show FF availabilty for all destinations available eg VNO & BER, call the contact centre for such flights. I usually call the contact centre a number of times before I book. I always check something with them on at least 2 occasions as you sometimes get different answers - some are very helpful, other can't wait to get you off the line.
I book as soon as the flights become available this is important for intercontinental flights - this changes from airline to airline, CX is the earliest & AA the latest. If booking on phone make sure you know all flights available to your desinations as sometimes they'll stick you one 1st flight that comes up on their screen & not the most convenient for you. In summary the most important thing is planning.
Enjoy your travels