A few tips

General

Ensure that you are fit. An assessment is a fairly intensive affair in which they are also looking to see whether you are a stayer, a go-getter.
Work with concentration. Show that you take the issue seriously. Do not think ‘oh, I can take care of that’. The assessors at an assessment are experienced behavioural specialists and they see through a lot; after all, it is their job.

Interviews

Ensure that you have a good idea of your own abilities and skills, as well as the job requirements.
Also, try to illustrate skills and characteristics with actual examples.
Also ask questions yourself, and try to make it an open and two-way conversation.
Do not talk too much, stick to the point. In an interview, you will also get the opportunity to go into findings from the assessment exercises and possibly refine these. Take advantage of this.

Intelligence tests

You can prepare for a test by going through a good practice book beforehand. This can sometimes help, especially with arithmetical series. Analogies and spatial awareness are (much) less likely to improve with practice.

Personality questionnaires

These do not usually present a problem. ‘Pretending' makes little sense; your real personality will still actually emerge in the behavioural exercises. Be yourself and, when completing such questionnaires, remember a work-related situation in which you feel most comfortable.

Role playing

Role playing situations examine various skills. Practice as much as necessary in advance, record your behaviour by using a video and afterwards examine the behaviour you display together with a reliable and competent person. Also examine your body language.

Final report

As an applicant, you are entitled to feedback. Even if the result of the assessment is negative, you can still learn from it. Therefore ask for a report of your assessment. This will help you prepare for subsequent assessments and provide you with more insight into specific strengths and points for improvement. Do not consider a negative assessment as a failure. There are many more aspects than a certificate, for example, which play a role in determining who is the most suitable applicant for a particular job. After all, an assessment does not have an infinite shelf life. Your competencies develop as a result of gaining day-to-day experience and taking training courses.