I started seriously studying in December of last year. I started with the NCEES practice test. Once I worked through about half of it, I started to get really worried because much of it was so foreign to me.
Then I started gathering resources and reading up on a lot of old concepts and formulas. I continued working through the test and started making a notebook of my own formulas. I had never even heard of symmetrical components before, so I really did't spend much time trying to learn the methods. That was definitely my weak point, and if I were to fail the test I would concentrate a large chunk of time to learning it.
I had searched the internet a bit to try and find a crash course on it, and that's how I discovered the Complex Imaginary site. I decided to get their 4 volume practice test and work through it as well. Even though I believe it has some errors, the practice I gained by working through the tests made them well worth the cost. Ultimately, I worked through the CI practice test twice each, and the NCEES practice test 3 times. I didn't have a strict schedule, but I easily studied 12 hours per week from December through April.
In terms of references, all I took to the test was my notebook of formulas, the NEC, the NESC, and Grainger's Power System Analysis. I think the PSA book helped me muddle through several symmetrical components problems on the real test. I work as a consulting engineer in the MEP field so I use the NEC on a daily basis. I had never heard of the NESC until I read a question about it in the practice test, but I ended up buying a copy just for the test, and I'm glad I did. I regret not having a reference on motors. There were a couple of motor questions on stuff I have never heard of.
Thankfully I had time to do the test, and work back over each problem again. I was surprised at the number of questions on the exam that were on material that was not presented in any of the practice tests I had done. However, working though the practice tests multiple times helped me figure out how to work my way through the exam when I didn't really have a clue where to begin.