QUOTE(Alicia Ocean @ Dec 31 2008, 09:12 PM)

The best advice is to get a teacher for the higher grades. I scraped through G6 on my own with much effort but then got a teacher for G7 and it was all made easy for me.
I would agree, but it's notoriously difficult to find a teacher for the higher grades. It's also expensive, as theory is very time consuming. I checked out answers for the harmony questions with my piano teacher, but I must admit that I resented the time taken out of my lessons, even though it was my choice to do so - I'd much rather be playing! Ideally a theory class would be the answer, but they seem to be as rare as hen's teeth too. For adults,
Benslow Music Trust run a course called Harmony for Beginners 2, which is for those with a basic knowledge of harmony and claims to be helpful for those preparing for theory grades 6 to 8. It runs from 21-23 August 2009, but isn't listed on the website yet.