Try not to worry too much about these details for how other folks did…it’s going to vary a lot, based on each person’s background: what they studied in school, how soon after graduating they took the test, whether they’re stronger in quant or verbal, etc. (It’s impossible to get a 628 on quant, btw. 620 or 630, but not a 628.)
Suffice it to say that if you take a practice test cold, without doing any studying at all, your scores are going to be pretty low. And that if you practice diligently and work hard to understand your weak areas and attack those, you will see a nice improvement. It doesn’t usually make sense to waste a practice test to get a baseline score, because that first score really is meaningless if you haven’t done any prep at all. Would you do that for a college class, walk in on the first day and take a test covering the entire semester’s agenda? Probably not.
I would suggest buying some of the prep books and just start learning about the test, practicing your math and English, and getting familiar and comfortable with it, before you take a practice test. It really is very tempting to take a test right away to see how you’d do, but you can freak yourself out if the score is really low and make yourself nervous about your ability to raise the score (lots of people here seem to do that!).
I started with Cracking the GRE, with the DVD with the practice tests. The DVD is cool because it has some interactive lessons on it, much better than just reading it in the book. I liked this book’s overview of the GRE the test. Very simple, easy to get through. The strategies are useful too, and the tests were as good as, if not better than, the official tests (they’re more up to date).
Download the official Powerprep tests too, from www.gre.org. Buy the official guide for practice questions. And get Word Smart for the GRE for vocab. The hit rate is really high with that book, lots of words that actually show up on the real test (unless you’re spending an extra month or so prepping and need to really beef up your vocab, I wouldn’t bother with massive word lists).
Hope this helps get you started…