Go for a book. Read it over a week or a month and find out the whole message of the book. That is how it is meant to be read, not in little pieces. Start to get to grips with the Bibles plot line. It tells a story.
Individual books fit into the story.
If you have never got into the Old Testament then you don't know two thirds of the story, and are likely to misunderstand the bits you think you know. Why not get someone who knows the Bible well to introduce you to an overview of the whole thing. You will be amazed and enthralled by the scope of God's plan to rescue people. Find ways to be accountable for your reading. Bible reading plans can be excellent.