Hi
Question that you should ask to yourself before beginning the prep are:-
1. Was timing a issue?
Soln: Start practicing more timed sets..grockit and
gmat club tests are the best source ...Devise timing strategy that suits you best.
2. Did you lack basic approach to a some type of questions?
Soln: need to improve on approach....search for approaches to those type of question....Karishma in Quants and Vercules or any other in verbal can help you...
3. were you nervous?
Soln: Take test more often.
4. Do you lack in practice?
Soln; Buy official official pack of question from mba.com or gmat paper test....
In a nutshell, if you have reached 600 that means you can for sure achieve 650 and 68 is just 30 points away from the mark ie.....Q 47 and verbal 34 so its not that tough ..you need to improve 3 points on quant and 6 points on verbal....e-gmat verbal live prep may help you...
By the way congrats on 150 points improvement........
Consider Kudos if my post helps!!!
Archit