How long should I preview lectures?

Hey there, I've been consistently scoring very high on my exams since beginning school. However, I am worried about my long-term retention and also getting the most out of every day I study. Should I try previewing lectures in the mornings when I start physio in January? For those that says yes, how long should I spend previewing each lecture? What exactly should I be getting out of the preview, I.e. Should I teach myself anything or is it more-so just passively flipping through the slides?... How long should I preview lectures?
Source: Student Doctor Network - Category: Universities & Medical Training Authors: Source Type: forums