Every employer is different and so each time you apply for a job you will encounter a different experience.  However, there are some things that are very likely to happen and the more you know about them the better you will do.

Many employers will design their assessment process around competencies (or the skills or behaviours that are required in the job).   So it is important you know what these are.  Typically, in the early stages or the assessment process, employers are likely to screen applicants through a telephone interview.  In later stages you will be interviewed face to face or may even be invited to attend an assessment centre. 

An assessment centre entails a number of different selection activities with a multiple number of candidates.  So it is likely you will be one of a number of candidates being assessed on the same day.  Assessment centres are usually competency based and so each activity will test the same group of competencies.  Typical selection activities are role-play, group exercise, interview, presentation, psychometric test, written exercise, in-tray etc.  Again, the more you know about these the better prepared you will be.