I'm not a LVN but I did have to study for a NCLEX test once
You'd be surprised at how much you have retained--you just need to dig it out!
In addition to the two review books I had purchased (Saunders and NCLEX Made Incredibly Easy), I went to the library and checked out every single NCLEX review book I could get my hands on. Then to study, I picked a subject (say, OB) and did the questions for that subject in each book. For the questions I got wrong, I reviewed the specific material in depth, and did a quick skim of the rest of the info. That way I reviewed but spent more time on the weak areas.
Also, make out a daily study plan for yourself. Don't expect to be ready to test in a week, but take a couple of months so you can review everything you need to and not stress yourself out.
I can't tell you what to specifically know for the test as I took a different NCLEX as you will be taking
And to be honest, I was told to know specific things for my test and almost none of them appeared on it, so who knows?