There is a famous book (some people call it "the bible") by Alex Moore, with the simple title "Ballroom Dancing," that you should read. (Alex Moore is English and the figures he describes are International style, not American, but his explanation of technique applies to all types of ballroom dancing.) There is a little section in the back of the book with the title "Expression in Dancing" that is what you want.
That does not mean you should ignore the advice others have posted about learning proper technique first. (Again from Moore's book: "The secret of the successful study of this book has nothing to do with the ability to remember such technical details as the numbers of the steps on which CBM, Rise and Sway occur. Rather it is the ability to understand why they occur." When you get to that point, then you may be ready for "expression.")
Our favorite dance instructor used to say that "Dance is a feeling."