It’s no secret. I think the New Testament is the greatest intermediate textbook when you are learning a language.
As soon as you are done with the grammar of a language, you are going to want something to read. Read the New Testament.
Here is the New Testament as an audio book in Latin: http://www.bible.is/LTNNVV/Matt/1
Click on the tab NVV in the upper left-hand corner and you will find the New Testament as an audio book in hundreds of languages.
I believe there are two great strategies to fluency in any language.
#1, Get into the country of the target language.
#2, Read extensively in the target language.
This site will give you plenty to read.