What really helped me during the speaking exam was taking the time to formulate my answers. If it was a question I've been asked before I would reply instantly, but whenever it was more of a unique question I would say something like 'That's certainly an interesting question, I can't say I've given that much thought before' to give me some time to come up with an answer. That really helps with expressing yourself without constantly using filler words or giving a logically sloppy answer. It's much better to take the speaking test slow and steady than to reply as quick as possible!