As an Ex-OBA'er - the way I did it was this - your milage probably will vary!
You don't need to have passed Air Law to fly solo - but you must complete an open book FAA exam akin to it before you go solo in US airspace.
First up - get a copy of the PPL Confuser. It's invaluable.
Second up - learn how to use the whizz wheel - there's some very good stuff in the Nav book on that - you will be shown how to do the wind/drift calculations at the Nav lecture at OBA (when I was there they did wind-down) - DON'T miss that one.
If you can use the wheel before you go, you don't need to worry about it later.
Met - this takes a bit of learning - I'd start on this one sooner than later.
Human Performance - the least indepth of any of the exams - you can study for this one in a day and pass it - especially if you've done biology at school or are aware of reasonably general knowledge stuff - how long does 1 unit alchohol take to leave the body/symptoms of CO poisioning etc/hypoxia etc.
Air Law - this one is a grind - I found the Thom book better than Pratt for this. Just start reading, and keep hammering it in until you've got it - it's a big memory exercise this one. Takes quite a bit of memorising to shoehorn it all in.
Dont bother with the Flying Training manual until you're over there, and read up on what you're going to do before your next lesson - it makes much more sense once you've thrown a spam can around for a couple of hours.
Nav - Nav becomes much much much easier when you've been to the lecture, and you've started planning out routes in real life. Leave that until later if possible and it'll save a lot of head scratching when you don't have the real world examples/experience.
OBA have the excellent lectures by Mike on Aircraft Performance/General etc - go to them, they're well worth it, be prepared for tales of intrepid hero pilots and bugsmasher 3000s, and athough they at first seem to sometimes digress, everything that Mike tells you will (or may be) in the exam, and some of his tips might just keep the shiny side up if you're in a jam (ie advice about encountering ice etc). Don't miss em (they're good entertainment!).
Also use the CD rom presentations in the study room at OBA - they're a good break for the books and are condensed into what you need to know for the exam, the books, especially the Thom ones, are much more verbose.
Comparing the Thom/Pratt books, I found the Pratt books easier to digest, but after getting the ticket and studying up again, I found Thom much more informative. I sold the Pratt books on ebay and kept the Thoms on my shelf.
Also remember (as mike will tell you) the object is not to just get the ticket, but to keep yourself alive, so regardless how you get through the exams, take time to go back an properly digest the subject matter at a later date - it might be particularly useful one day in a tight spot! The licence after all is a "licence to learn"!
Oh, and learn conversions - 1nm = 1.15sm = 1.85km and distance equal to one minute of arc on the Earth's surface. 1 USG of Avgas weighs 6lbs. 1 USG = 3.75 litres. Or learn how to use the whizzwheel to work them out.
Remember - no calculator in the exams, so if like me your mental arithmetic is sometimes quite mental, learn how to use the whizz wheel for multiplication/divison to get the solution (or at least an idea if you're right or not)!
Above all - enjoy it! It's a fantastic place to fly. (And drop in to see the Tower guys - they always welcome visitors
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