I used the "OH MY GAWD
I AM GOING TO PASS THIS TEST METHOD".
I used QRZ as a pre-assessment and then I used the "Subject categories" in the Extra pool and studied them one one at a time until I got 100% and then moved on to the next one until it got to be very monotonous. Then I started skipping around to the subjects that I felt I would have the most trouble with as much of the Extra test is a review of the material for the Tech and General license.
I also studied the ARRL Extra Study Guide. I found that to be of very little value as I felt like someone was awfully proud of themselves with all of the complicated math they could put on one page without actually teaching me squat. I would refer to it every once in a while and it would help some but it was definitely worth the cost.
As I progressed through the material on the QRZ site I would go to the AA9PW test site as the tests were set up most like the actual tests.
http://aa9pw.com/radio/This seemed to be a better indicator of how well I would do on the real thing.
There was still too much I was not grasping. Either it was because my head was too thick or the material was not presented in a way that my thick head could absorb.
Eventually on the QRZ and AA9PW sites I was getting consistant 75-84%. I was still failing every once in a while and it concerned me because there was the math and formulae that I could not remember and with a pool of over 700 questions I was not able to remember the answer all of them correctly. Often the questions were very close each other with different correct answers.
I had signed up for a trial at HTOL but I was wrongly using it as a test resource and I later found that was a waste of time for that purpose unless you pay for the subscription as they only give you 50 questions of the pool while reminding that you have not completed the signup process.
Eventually after reading the great reviews that others had said about the HTOL teaching and learning process and how many went from ZERO to EXTRA in one session, I signed up and followed the recommend process to a point. At first I I felt like I was doing the QRZ subject study again until HTOL started beating me up over the questions I had previously missed during the study sessions. Much of the sessions were very well documented and some of the stuff that I earlier could not get my head around I finally started to get. However some of it took creative processing on my part before I started to get some of the tougher questions saved in my brain.
I also decided to get some applications and podcasts for the Extra test from iTunes (for the iPod Touch) and through the discussions I was able to gain even more. I was lucky enough to have a friend that had got his Extra about 2 months ago so went to him for explaining some of the more difficult concepts and the some of the math behind it. I was great having a real live teacher.
I saw that my tests were becoming more consistant but there was a TON of material that I did not know yet many of the trick questions. I had 2 days to go before my next opportunity to visit with the VEs. I decided to go against the HTOL recommendation and do some cramming. I spent 20 hours of the last 2 days prior to the test in HTOL alone with.
In my opinion it is perseverance that will get you to a PASS. I know you can over-study and I know you can be too confident and end up with a batch of questions that you have never studied as well. In my opinion HTOL is second best resource for learning what you need to know to pass the test. That is second only to a real live teacher that has freshly passed the test with a good score. If you can find an Extra that has a good understanding of building, setting up and correcting antennas and the issues that arrise you will learn a great deal towards the test. I would still get HTOL as a back up for retention.
If you have subscribed to HTOL and you are using it you will be advised that some of the material may be skipped as your chances of seeing some of the questions may not be on your test. I WOULD AGREE. Skip that stuff and come back to it after you have learned some of the other material. Don't feel bad about skipping any part while using HTOL as you will be reminded to go back and learn it.
Also this is very important... Stay away from the temptation to test multiple times a session. Taking a test is too stressful after learning so much stuff at one time and you may not pass it. Doing so could mess with your confidence.
Do not stress too much on the math. I would learn the RMS material as it pertains to feed lines as you will be using this one day if you ever have to make an antenna from crap you find. Actually I would learn everything you can but much of may not be needed.
On the day of your test I recommend that instead of pretesting that you study the material that you have the hardest time with at the QRZ site and see if you get 100% on those subjects. The only 50 question test I would take that day is the real one.
Pass the test and then keep working on the material at HTOL.
If you fail, keep a mental note on what you may have missed on and the come back around the next time you get a chance.
The big thing is to keep hammering at it like a bird building a nest, one tiny stick at a time until it is secure enough to rest on it.