The best way to keep the listener engaged is to engage them meaningfully from the very start.    There are a number of techniques to do this, including beginning the podcast with a compelling quote, question, or statistic that immediately immerses the listener in the content.   Personal stories or colorful ancedotes are also great ways to creatively grab the listener’s attention from the get-go.
To keep listeners engaged throughout the Episode, knowing the their knowledge needs and reminding them of why the content is important is critical,  However,  it is often helpful to break up the discussion in a way that refocuses the listener. This can be done by addition music or sound effects between blocks of conversation, or summarizing a topic or set of topics before moving to new “chapter”.   If you employ advertising in your podcasts, they can be used in a similar fashion.