I would advice you to spend some time on prep for the General test too - of course you should concentrate big time on the PhysGre but still, you shouldn't completely neglect this one too, as having to re-take the test could be an unnecessary waste of time, effort and money.
depending on how you feel about vocabulary, reading compreh, and writing essays - big "?" here is if English is your first language here - I would advise you to at least look at prep tests and one of the prep books by Princeton Review, ETS, Kaplan etc and the likes for some extra exercises and advice ... especially those lists of most frequently used words, which I found very helpful and it was almost scary how many of those words came up on the test I took
. My advice is spent at least 7-10 days going over those and just getting familiar with the overall structure and dynamics of the test, especially if you are an international student and are not very familiar with GRE-like tests.
as for the math part, it's extremely easy concept-wise, at least the vast majority of it, however, my advice is to spend some time on prep for that one too as you might find it a bit tricky when it comes to solving those problems under pressure with time running out. You may well know how to solve all problems in general but on the GRE you need to do that quickly and efficiently too and doing some extra prep may well give you some useful ideas of how to do that too.
This being said, PhysGre is the test to spend most of your effort on.