Just be yourself. Polite, focused, listening skills are very important. And never interrupt the speaker.
Keep applying since i had 2 times applied, before i got accepted.
Be relaxed and sound professional.
Be patient after applying it could take a while before getting a call back. Once they give you a date for the exam study the material they send to your email.
Be honest. If you aren't available everyday they won't penalize you for it. I worked full time during the day and did this in the evenings and weekends.