I honestly think you should have completed the
MGMAT books in order (i.e. start with the quantitative books). If you have not completed the OG problems that
MGMAT recommends, you might as well just go through the verbal books again. If you decide not to, I would go through the quantitative books and the refresh yourself on the verbal section. Some people recommend taking a GMATPrep test halfway through your prep, but I disagree. I saved both of my GMATPrep tests for the end.
If you are using the 5th edition on the
MGMAT guides, you will the OG 13. OG 12 is meant for the 4th edition of
MGMAT. I would suggest getting OG 13 because of the aforementioned reason, but also because it includes IR prep. Have a look at
this thread for some more IR prep.
I hope that helps