I am sorry to know that you could not achieve you target score even after 3 attempts. How did you prepare for the exam. Regarding strategy for 680, I recommend that you view the recording of my strategy session below.
Recording link: Click here
You will get to the recording as soon as you register.
Aiming to score 760+ on the GMAT? Attend our free webinars to learn how to:
[*] Master Number Properties
[*] Ace Critical Reasoning
The webinars will start at 7 AM PST on the 11th and 12th of July, 2015.