What do you need to do?
If you have an idea of what competencies are being assessed, try to think through what behaviours make someone strong in that area. Eg. For 'Working Collaboratively', behaviours might include: addressing others by name, acknowledging what others have said, using eye contact effectively etc. For 'Applies Critical Analysis', behaviours might include: considering all factors; looking at problem from multiple perspectives etc.
Try to be yourself and demonstrate your own unique qualities and skills. It is worth remembering that you are not competing against other participants, but rather being assessed against the competencies set by the organisation. If all eight participants have demonstrated the competencies then all eight may be accepted through to the next stage.
For presentations, remember to structure your argument to get key points across within the (often tight) time allowed.
Be well attuned to the values and goals of the organisation. Often the competencies for the role are in keeping with the core values.
Remember to take photo identification with you - check your invite for requirements