need a good study plan

I'm in no time crunch to take the GMAT since I'm not applying till next fall. However, I've started studying to get it out of the way. I haven't set a target date because I don't want to rush my studying and I want to give myself as much time as I need to prepare. I imagine my general target is several months from now... end of the year or early next year. However, I'm not sure what type of schedule I should go with in terms of what to study. Currently I've taken a practice test and have gone through the problem solving guide in the Princeton Review book. Now I'm going through the problem solving questions in the OG. Prob about halfway through. Should I just tackle each GMAT section one at a time? Or while I'm grinding through problems in one section, mix it up a little by reviewing how to do other sections. My concern is that if I do one section at a time, and do all the problem solving for example then move onto the next one, by the time I'm done with all sections in a few months, I'll have forgotten how to do the early sections. If I just confused you, I apologize. But in short, I need a good study plan for someone whos taking several months to study. Fwiw, I got a 600 on the diagnostic, shooting for 720ish.