I disagree with the approach of "letting the bible interpret itself". It has proven over and over to lead to pitfalls. The very protestant tenet "sola scriptura" didn't result in a unified interpretation, but rather, in thousands of different interpretations, all claiming to be "bible-based". Your best approach is to let the author of a particular text (book) interpret itself. And then consider where is he coming from, what are his influences (in many cases, these influences are to be found outside of canonical scriptures), and of course, what was the motivation of the writer, his political and religious agenda, and to what audience he was writing for.
To simply start off by assuming that the writing hands who wrote the texts that comprise the [protestant] Bible were in harmony with each other is to ignore solid textual criticism evidence and start building over a basic mistake.
Want a simple example? The writer of the gospel of Matthew misreading the Septuagint translation of Isaiah 7:14 to conclude (wrong) that Jesus surely must have fulfilled some prophecy of being miraculously born off a virgin, wholly ignoring the historical context of the episode; and hence how the story of a virginal birth was concocted and gained traction. (The author of Mark, the oldest gospel, knows nothing about a virginal birth story or any other fanciful Jesus infancy stories, btw ...)
