i just took them on friday and couldn't be happier to have it over with, but here's my general impression of the whole process.
i used the princeton review book to study and i thought it helped a lot. a lot of good tools for making educated guesses, and the online practice tests are clutch. i'm the opposite of you and i'm really comfortable in math so i focused my studying on learning vocab, and i saw noticeable improvement over the month leading up to it. even if you think you're good at english, study the vocab as much as you can, especially because the verbal is scored easier than the math. this will help pad your score a little bit if you can ace it. as for the math, my test was SUPER geometry heavy. everyone told me to study formulas, which i blew off, and was glad i did. know how to take the areas of stuff, angle properties of various shapes, and practice basic algebra and you'll do okay.
in general, i thought by far the most helpful tip i got was with pacing myself. the way the GRE works is each question is a different point value/difficulty depending on whether you got the previous question right or wrong (which you probably already knew). but, its weighted really heavy towards the first half, so take 2/3 of the time to really work through the first 1/2 of the questions in both sections. this will set you in a score bracket that you're kind of stuck in regardless of how you perform in the second half, so it doesn't matter if you have to rush the later questions.
as for how much your overall performance really matters, grad schools don't really care about your GRE score as long as you're over the minimum threshold. of the schools i'm applying to, MIT had the highest minimum at 1200, so you're probably not going to see much above that. don't sweat it too hard, but take the time to study and do well the first time. apparently it looks bad if you have to take it more than once and i heard (although i don't know for sure) that they average your scores instead of just taking the highest like the SAT.
anyway, that's a pretty long winded insight, but feel free to throw more questions my way.
oh, and if you're comfortable with english/verbal, don't bother writing practice essays. it'll be a waste of your time.