... do you want to know books written by Tolkien himself or books about Tolkien/Middle-earth?
The only books Tolkien published himself are The Lord of The Rings and The Hobbit; he also finished the Silmarillion, but it wasnt published at first.
Christopher Tolkien, his youngest son, later published more of his father's writings, but no more complete stories.
The easiest ist probably the Unfinished Tales;
The History of Middle-earth contains twelve books (War of the Jewels ist one of them, as well as the two Lost Tales) which show the earlier forms of the legendaries of Middle-earth, not really new stories.
Yet I think it's quite interesting and informative, but only for hardcorefans.
The order - well, it's just the other way round than most people read it 😛
The last is the Lord of The Rings (well, the New Shadow is far too short to be counted as an own book), before comes the Hobbit - these two play at the End of the Third Age.
The Unfinished Tales contain information mainly about the Second Age, but also interesting stories about the Third Age and also the First Age.
The Silmarillion is the most important book, it gives an overview about neary every story of the First Age of Middle-earth and the time before time.
The Histories just give other versions of these stories (mainly the Silmarillion, but also four books about the Lord of the Rings).