Like many others, I sat the 'easy' ones first. This worked well for me. I'd highly recommend sitting performance and loading before flight planning, as intimate knowledge of the 727 that you can recall quickly will be beneficial for flight planning. Nathan's method (i.e. the CASA method) and tips (e.g. 5 markers first) worked a treat first time but there are other resources out there in addition to AFT that can supplement your exam readiness, e.g. Rob Avery notes and practice exams and ATC. I have never sat his course (though I've heard good things) but there's another guy out there, Dr Steven Holding from the College of Aeronautical Science, who offers a completely different method for flight planning. Understand he also offers ATPL nav.