Find out as much as you can about the test before the day and, if appropriate, ask if there are any 'past papers' to practise on.
Have a good night's sleep before the test and eat a healthy breakfast on the day.
If there is going to be a numeracy/literacy/reasoning component, practise doing these types of questions.
Read all instructions carefully, even if they seem obvious to you.
Don't be afraid to ask questions to the administrator.
If you're taking the test online from home, wear smart clothes and shoes and sit upright at a table to get into a business frame of mind.
Don't skim the questions to scope what looks easy or hard at the beginning; just move from one question to the next, pacing yourself.
Don't dwell on one question for too long – if you're not sure, leave it until the end and go back to it.
On personality components be honest and be yourself. Don't second-guess what the company wants you to say and don't attempt to cheat (they have ways to catch you out).
Don't worry! Even if you flunk the test, you're still in with a chance as the hiring decision is based on a combination of your resume, interview performance and presentation, work history and test results.