Have a good look around at available school and go with a recommendation or your gut. As was mentioned...never pay for more than 5hrs upfront to get a discount. Pay as you fly is safer.
I instructed for 3years and the only way really is a 3-4 lessons per week. Anymore and you risk being overloaded and the fun goes, any less than 3, you are playing catch up on things you have forgotten.
Read the manual that your school use before each lesson, and get the plan in your head before you walk to the aircraft. Any foggy bits are best sorted in the briefing room or hitting the books before hand.
Try and get your air law and nav exams done ASAP, as you could be going solo in 8-12 hrs if the conditions are right (about 2-3 weeks). The exams will hold you back and cost you more $$$
PPL Training
I used to teach from this book as it's very well explained and kept simple.
There are lots of mock question books for the exam papers, so read the book, then hit the past papers - I only know where to find the UK JAR ones.
http://www.faa.gov/training_testing/...SampleExam.pdf
Pilot Practice Page
Spend time learning your emergency drills:
Smoke - oil and elec
Fire - on the ground, on take off, in the air.
Failure
Blocked runway
X-wind out of limits
Again, this sharpens you up for quick progression. You need to be safe. I would always ask...would I put my kids in the aircraft with you?
Flying is half of it; the other is attitude and as has been said, a great deal of learning is done after your licence. Get instructors to set you tasks, or places to find with a diversion - really give your brain a workout.
Good luck!