The experience and skills come across through the CV of a candidate. But the recruiter wants to know "more" about the candidate. The candidate's ability of lateral thinking and reacting to different situations is what can be included within the "more" tag. this is where Psychometric Tests come into play. 

Psychometric testing falls into three main types :

Ability testing 
Aptitude testing 
Personality testing

ABILITY TESTING: Ability tests measure a persons potential, for instance to learn the skills needed for a new job or to cope with the demands of a training course. Ability tests are prospective: they focus on what the person is capable of achieving in the future or their potential to learn.

APTITUDE TESTING: Ability can be viewed as underlying aptitude, and aptitude as being more job related then ability. Aptitude tests tend to be job related. They are concerned to find out how well candidates perform in reasoning tasks. In other words, the recruiter is looking at the level and nature of your thinking abilities.

PERSONALITY TESTING: Personality can be defined as - 

Those relatively stable and enduring aspects of an individual which distinguishes them from other people, making them unique, but which at the same time permit a comparison between individuals.

When we discuss personality we must remember that it is not a single independent mechanism but closely related to other human cognitive and emotional systems.
Personality questionnaires are concerned with how you typically tend to react or behave, and your preferences or attitudes. 

HOW TO PREPARE FOR PSYCHOMETRIC TESTS:

Having a go at puzzles like word games, mathematical teasers and puzzles with diagrams can give you some practice. It may also help if you brush up on your basic mental arithmetic. Practising puzzles against the clock can help train you to work both quickly and accurately.

If starved of food, the brain can be sluggish, so on the day make sure you eat breakfast and perhaps some chocolate about an hour before the test (although not liqueurs - save them for when you get the results)

You can also try out some actual aptitude tests for practice.