Hi BurakOz,
A score goal of 600+ is reasonable. We need to get a better sense of your current strengths and weaknesses though.
To start, we need to establish a 'baseline score' for you so we have a basis for comparison and an idea of what you'll need to work on. This will require that you take a FULL-LENGTH CAT test. If you've taken one already, then great - what were your scores? If you haven't taken one yet, then you can download 2 for free from
www.mba.com. A FULL CAT takes about 4 hours to complete, so you should make sure to set aside enough time to take the Test in one sitting. If you want to do a little studying first to familiarize yourself with the types of questions that will appear on the CAT, then that's fine, but you should not wait too long to take that first CAT.
Once you have your first set of scores, you should report back here.
GMAT assassins aren't born, they're made,
Rich