Hi desertEagle.
Most schools don't care very much about IR. So, an IR score of 6, or even 5, is good for applying to business schools.
However, there are some employers, such as some consulting firms, that consider IR scores in evaluating applicants. So, if your planned post MBA career path might involve such employers, you may want to score 7 or 8 on IR.
For the most part, you GMAT Quant and Verbal prep will serve as your IR prep. However, there are some additional things you can do to prepare for IR.
For detail on how to prepare for IR, see this post.
GMAT Integrated Reasoning Tips