Dude, I'll totally take the vocab portion for you if in two years you take the math portion for me... because in that area I am F U C K E D. I don't think I've had a math class since 1998, and that was special 'integrated' math my school district adopted to get us less gifted mathematical people to pass the state requirements... about the only thing I learned was how to program games on my graphing calculator, and even that I don't remember much of.

Don't forget breakfast, deary

From the standpoint of someone who does grad admissions, I can tell you that some people find it very distressing how much the preparation programs help. That is, especially if you take a prep course (if you have the money). I imagine the books work well too, but I have personal knowledge of people who upped their scores a lot doing the courses.

Study.

The basic GRE is cake. It's the subject one that'll leave you crying. Take some practice tests to get a feel for what you gotta study hard.

Don't study to hard it doesn't matter really. I took it with a hangover, and I did very well.

I studied to try and boost it, and it went down. So, there you go.

You seem sharp. You should focus on the subject test.

FOR THE PHYSICS GRE:

Get a book of the old questions and go through them.

Take the test once timed without studying. Figure out what you don't know.

You will need:

Griffiths, Sakurai, Goldstein, and Griffiths EM.

Focus on quantum mechanics, classical mechanics, and E&M. The quantum questions are easy. E&M and Classical are hard.

Go through the test with your friends. Work through them slowly. Figure out what areas they are trying to test you on. Review those areas intensely. Invariably, there are scattering questions, and even though it is the toughest topic in introduction to quantum, you need to nail it down. The other areas are pretty obvious.

Know some basic math tricks. Like integrating a guassian to a given power, etc. Know how to integrate by parts quickly.

When you are done preparing for the physics GRE with you friends, and I encourage you do it in a group, take the at least 2 practice tests timed in a battlefield scenario.

Now you are ready to do battle. Unfortunately, this is the second to last test in your entire life that actually matters.

Don't take it with a hangover. Take it seriously, and you will do OK.

About the scores... Here is essentially what the gist of the advice I got and my experience in grad school.

The average American score is in the 50% most years, so that is considered good. The smartest person I have ever met in my entire life told me he got a 76%. In contrast, every Asian(Indian, Chinese, etc) student who I know the scores of got over a 95%, three got perfect scores and they said this was common. Don't expect anything above an 80%, if you get above an 80% consider yourself lucky, but it doesn't really mean anything if you don't. Two people in my class who got above an 80% also failed the qualifier. Your goal should be to get above the 35%. If you don't break that, then you should worry.