The TOEFL (Test of English as a Foreign Language) listening test involves a 5-minute-long lecture on a variety of subjects and topics. In The Official Guide to the TOEFL Test, it states the aim of the listening section is to test whether you can get the important details right, not all the details right.
My question is: How do I discern important details from unimportant ones in the TOEFL listening test? To be more specific, What are the logic traits or language context of important details?
For example, whenever the professor refers to previous knowledge on a certain topic, details are not important, because the questions are usually involved with what the professor implies by mentioning previous knowledge, or the rhetorical meaning of it.