This is the best book out there for mastering conversational Spanish. If you doubt it, compare the 250+ Amazon reviews for the 1994 edition with those of its competitors. I got a lot out of it when I was new in Mexico and I still remember much of its specific advice.
Perhaps a more honest title would be Breaking Out of Intermediate Spanish; the ideal reader can already hold their own in a conversation. Even so, advanced beginners should still find useful tips. The author does a reasonable job of handling regional differences, an unenviable task.
By Joseph J. Keenan. University of Texas Press. 20th Anniversary Edition (2015) ISBN:978-0292761933.