Even though aptitude tests are taken under exam conditions, as with any part of the job-seeking process the more time and effort you put into your preparation, the better your chances.
The employer or recruitment agency may provide you with a sample of a previous test, and it’s worth asking for one even if they don’t volunteer it. Depending on the job you’re going for, you should have a general idea of the kind of test you’re likely to face (i.e. whether it’s verbal, numeric, abstract or some combination of these). A quick search online will turn up no shortage of sites offering suitable practice tests, some free, others charging a small fee. University careers websites are another good place to look.
Other ways of getting into the mindset for an aptitude test include doing word puzzles or maths puzzles in the run-up to the test, pushing yourself to go as fast as possible against the clock. Reading sample questions will also give you a feel for the sort of language used. Always make sure you understand what the question is really asking for before starting to answer it.
Treat the aptitude test in the same way as an interview: if you’re taking a test on-site, set out to arrive with plenty of time to spare (arriving late will do your prospect of success no good at all); dress professionally (while appearance might not be on the test sheet, an examiner could take one look at you and cross you off the list); remember to bring glasses if you need them; and make sure you arrive fresh and focused after a good night’s sleep.