Hi, don't be disappointed, there is always a next time to improve. I'm sure that while you were preparing for GMAT you must have come across many loopholes or weak areas in your preperation. either you had not given complete attention to your weaker points and focused on stronger area. moreover if u were getting 700+ in tests and got 670 in mains then it shud not be such a setback to you as there is a difference in the main exams and mock tests, u r under more pressure, difficulty level is different. Either you were not using the write test material, were overconfident, or at times it happens that if you did mistake in the initial Questions you hampers the score.

So now focus on your weak points and get hold of some good material like Kaplan test material, or you can even go for the online tests available which are in the same pattern as main GMAT .

So now do not study too much as it will eventually wear u off, just focus on weak points but at the same time do not neglect strong areas.

All the Best , i;m sure you will hit really good this time