It is my personal belief that to increase your IELTS oral score more than good grammar, perfect tense, good fluency and good English usage and understand are needed. I believe that the Examiner is also trying to see your ability to adjust to western culture. As you see more and more questions are being asked concerning opinion, your attitude toward a specific subject etc. It is my belief that the higher scores are attained by the best speakers as well as the best culturally influenced candidates.
Eye contact is the most important. You should look at the examiner eye to eye. Now if you have any difficulty doing this, look at their noses. Thats right, their noses. Looking at a persons nose is the same as looking them in the eye.
Smile. I know it is difficult in this situation, but try at least to smile and express yourself.
Head movement is also quite important. When you are asked a question by the examiner, if you understand the question, nod your head yes and then answer the question to the best of your ability.
Hand gestures are also very important. Use your hands to make a point etc. Just do not sit in your chair like you are a motionless being, show some enthusiasm.
Body language is also important. Sit up straight, look at the examiner, smile, use hand motions etc. Do still on the chair like a bad of rice, so some movement, some life in your body.