Psychometric tests look at skills like logic, numeracy, technical ability, literacy, verbal reasoning, inductive or deductive reasoning, spatial or diagrammatic reasoning, situational judgement, motivation and personality.
Larger organisations often consider a number of candidates together using a range of tasks, such as psychometric tests, group challenges, role play, presentations, in-tray/e-tray exercises and interviews.
Assessment centres are carefully designed to see which candidates fit the role and the organisation, so they may be considering your personality, your approach to solving problems and dealing with situations, leadership potential and overall ability to work in a team, and your commercial awareness, as well as further testing your skills and abilities.
Prepare as you would for an interview: dress and behave professionally, be punctual and bear in mind that everyone you meet on the day may be asked what they thought of you.
The following resources offer free practice tests, but may also contain further resources or tests at a cost.