Generally book about 4 to 6 months in advance, travel during school holidays, and for 4 people. Example trips in economy are BNE-SIN Sep holidays, BNE-SYD-Shanghai Jun/Jul school holidays. Had booked in Feb this year again for BNE-SIN in Jun/Jul holidays for 5 pers and they requested and found seats direct one way and through Perth coming back. Check seat guru and see what inventory is available and when you ring ask them if they can request release of seats for another day. Downside is you do pay assited booking points.