How can I prepare sufficiently for the competency assessments?

As with all exams, you should ensure that you have adequate rest the day before. During the assessment, take breaks in between papers (if you are taking more than one) to minimise fatigue. 
 
At the very least, you should have read through the preparatory guides for the Papers that you are sitting for, in order to get a better understanding of the question formats. 
 
Check the paper’s time limit before beginning to ensure that you have adequate time to complete each section. If you are taking the assessment remotely, check and mitigate technical problems or distractions the night before to minimise disruption during the assessment.