The most important IELTS speakinig tip is quite simple: practice, practice, practice! This is the best, easiest and quickest way to improve your English speaking skills and therefore your performance in the IELTS speaking test.
With lots of speaking practice you automatically become more fluent and more confident - even if your vocabulary and grammer aren't perfect. Other tips to improve your IELTS speaking skills include learning new vocabulary related to each topic, recording yourself to become more aware of aspects of your speaking which you can improve, and learning to organise your ideas well when speaking.
But the quickest way to become better at speaking is - speak more, speak more often and speak about IELTS topics. Find a speaking partner and practice as often as you can, you can use the examples in the IELTS speaking questions download to start improving your IELTS speaking skills immediately.