Fluency in ESL has a slightly different meaning from fluency in general, which is facility in the use of a language. In ESL, it is restricted to speech and refers to the speaker's ability to link language units with reasonable ease and speed. 
In the seventies, it was popular to teach fluency using substitution drills. Starting in the mid 80s, a notion of message-focused fluency emerged, where fluency was considered facility in using language to express a message. In this view, form is not important as long as mistakes do not get in the way of the message. In particular, Brumfit (1984) described how to make a fluency building activities. These activities should focus on the message, have a message determined by the student speaking rather than by the teacher or textbook, and proceed with minimal teacher correction. 
- Hedge, T. 1993. Key concepts in ELT ELT Journal. Volume 47, Number 3. pp 275-277. Oxford: Oxford University Press.
- Brumfit, C. 1984. Communicative Methodology in Language Teaching: The Roles of Fluency and Accuracy. Cambridge: Cambridge University Press.