I personally feel that the GSP's are very poorly written....I prefer reading up from oxford for better understanding of the topic...The matter is well written and includes some humour here and there....
For examination point of view go through question banks e.g. Pooley's, volare, PPSC ( i am trying to find this one out....last attempt tech. paper was from this one )....
Websites like exams4pilots (Met. last 2 attempts) and turbinesturbines
The list is long....So get your hands on as much material as you can and keep reading everything you lay your hands on.
If there is any specific topic you need info on, Let me know, I'll be glad to assist with regards to the reading material...
Cheers
P.S. CP PNR questions are still being asked...Flight planning not so sure..