Schools are going to want to see that you at least attempted the IR section and as time passes your score on this section is likely to become more important. I would say that you would want to be at the 50th percentile or above in order to show your effort. That means getting a 5.0 out of 8.0.
In order to earn a 5.0 you need to get maybe half of the questions right -- so 6 correct out of 12, something like that.
As for how this score is used in admissions, for now the IR is mostly a hurdle that you need to get over. You do not want to get such a low score that you give admissions committees a reason to reject you.
With that said, I typically tell students a few things:
1) You may want to attempt 10 questions instead of all 12 (meaning that you would just quickly guess at 2 of them), this will give you 3 minutes per question instead of 2 minutes 30 seconds.
You can pick the question type that gives you the most trouble or you can just look for the toughest looking problems on test day. Be careful about skipping multi-source reasoning though- usually 3 questions are based on the same prompt so it does not usually pay to skip (quickly guess at) one of those unless you are skipping all three.
2) Think of this as a warm-up. If you are agonizing over the questions on IR you may be lowering your score on the Quant and Verbal section by getting tired. So if a particular question is really confusing you then guess at that one and move to the next one.
3) Practice the IR enough that it is not painful for you and you can get at least 6 questions right without tiring yourself out. Not practicing the IR enough is a problem for many people not only in that it results in a low IR score, but because it can also start the test off badly and wear out a test taker or demoralize him.
Happy studying!
