Many threads/posts on this. Just don't be a jerk. There are many cautionary tales but the take-home message is that if you are the type of person who is conscientious that it is humanly possible for you to do something that might make you DNR'd (i.e., if you are a normal/reasonable person), the likelihood of you actually being DNR'd is essentially zero. The people who get DNR'd are people who are unable to hold a series of short conversations with strangers without annoying, offending, or scaring multiple people.
To put it another way: if you got invited to second look, just act the way you acted during your interviews.