First of all, let me note that the notion that anyone should read the Bible is a deeply Protestant notion. It is only when you take the Bible as authority that it becomes really important to know the thing.
Second, the notion of the Bible as a whole is something that would come as a surprise to anyone of Christ's time or Saint Paul's time. It just never was intended to be a single authoritative document that told you everything you needed to be a Christian. I've written about this before.
Isaiah Berlin made a famous distinction between foxes and hedgehogs based on an old folk proverb: "The Fox knows many things but the Hedgehog knows one big thing". People who insist that we read the Bible are hedgehogs and they imagine that the Bible itself is a Hedgehog with one big truth just like them. Luther with his sola fide is a good example of this. The Deuteronomist historian is also a hedgehog trying to establish that the Bible events fit into the same pattern over and over again.
The Bible, however, stubbornly resists Hedgehog interpretations. It is the work of so many authors in so many situations that it could not help but be. And Jesus himself is a Fox. He comes to preach good news to sinners and he does so in a variety of ways and situations. And, if you agree with me that the Bible is inspired by the Holy Spirit, the message is definitely not a coherent whole. We have four different perspectives in the Gospels and several others in the letters.
Is there one big idea? Yes, I believe there is but it's not the Bible. to paraphrase Anselm, if you believe in God the Bible will help you understand. If, on the other hand, you seek to understand the Bible in order to be able to believe you will most probably fail.
So how would I advise people to read the Bible? Read the bits that speak to you. Don't close your mind as to what they might be—I was surprised and pleased by how much positive inspiration I found in Leviticus which, despite its reputation, is one of the most beautiful and inspiring books in the Bible. I read Isaiah because it is so important to later biblical authors but I have to confess that it has never been anything but pure drudgery for me to read it. I read some books—Leviticus, Ruth, Proverbs, Mark, Matthew, Corinthians, Ephesians, James—over and over again. Others—Deuteronomy, many of the prophets, Romans, Revelation—I read only when it feels absolutely necessary to do so (typically when I am looking to check on some claim I've read somewhere about what is in these books).