I was preparing a student for IELTS Speaking earlier this week. We worked on his spoken fluency and spent a great deal of time expanding his range of productive vocabulary.
At first, I used the techniques of rephrasing and upgrading from Thornbury's Dogme Approach. It seemed to have worked by the middle of the week. This student would always hesitate and search for language before he spoke more fluently on repeating the same task.
However, candidates don't get a second chance in IELTS Speaking test. They must be able to perform well on the spot. So I decided to introduce another technique. Using a topic-based approach, we looked at the vocabulary banks of some Advanced-level coursebooks. With substantial pre-task lexical input, this student should be better able to use a wider range of collocations and a more precise set of vocabulary. Perhaps you can already tell what I'm going to write next by my choice of 'should'.
Finally, I introduced yet a new technique which I had never tried before teaching this student. I asked him to lie to me - give me 'false' responses to a set of Part 1 questions - and he shouldn't say anything true about himself or others. Eureka! This did the trick of liberating his formulation process; he was subsequently able to speak more fluently. I guess it's easier for most people to talk about something they already know but more demanding to invent ideas when they're speaking. The opposite holds true for this student!
Note: Candidates need not say what they honestly think in IELTS Speaking. It is a test of one's language ability.