Hi Leviathan, it is possible to get from 630 to 670. Just make sure you have a copy of the OG and go through it in detail. Kaplan800
will also help you but remember that you have to go through every question in order to understand why you got each wrong AND right. I would suggest you to join the GMAT challenges in the next weeks; there is one given once every 2 weeks. Also, go through the explanations in the "best of verbal" forum as you will see much interesting discussions there. Participate in this forum as it will be your best bet at getting a good score.
PS. If you have not already done it, go through other people's experience in the "share your experience" section. There is much to learn from others' experiences. Good luck.