http://www.excellerate.co.nz/personality_test_success_tips.html

Personality tests used in an employment context provide recruiters and prospective employers with information on the person-to-job fit; how the candidate may fit within a work environment, how they will work with others and their performance potential against job requirements.

The first thing to remember is that you can’t pass or fail a personality test. There is no such thing as a right or wrong answer. You are who you are.
In an effective selection process, it’s only one piece of information, not the complete picture. The combined results of the selection process are used for the final decision.
Familiarise yourself with the instructions on how to complete the tests and note that you’re usually allowed to do some practise questions beforehand.
Most personality questionnaires will ask you to consider how you typically behave in a work/public setting so don’t consider home or private situations.