Here are a couple pieces of advice I would offer regarding how to choose what to study....
1. During the first part of your test prep, allow yourself to study what you're interested in.....at least some of the time. I set out trying to stick to a very regimented study schedule and started going crazy pretty quickly into trying to read through the ACI. I read some advice on this site that really helped me out. It was something like, if you can find a way to make yourself enjoy your preparation, you will do a lot better. For me that meant jumping around a lot, if I came across something at work about wood shear walls that piqued my interest, I would let myself look over that that night, even if concrete was on my schedule. My thought was, I have to cover all of it anyway, so if you have a desire to learn about something at some particular time, just do it. My retention is a lot better when I am interested in what I am reading.
2. On the flip side, do keep track of what you have studied and do not leave any holes in your knowledge. I completely agree with TehMightyEngineer. Nothing in the ACI, AISC (and SZ provisions), NDS, or TMS is too obscure to be on the test, especially for the lateral because there is significantly less material. When I took the exam, one of the lateral questions asked about a type of member that I had never even heard of before the exam.
Hope those things don't seem contradictory, they are just what I took away from my experience with the exam.
Good luck!