Between now and the test session:
Revise your school algebra and trigonometry.
Do word and number puzzles, and simple crosswords.
Practise with lots of examples, but don't use a calculator.
When practising, set yourself time limits.
Immediately Before the test session:
Get plenty of sleep the night before.
Find out exactly where the test venue is and check what time you have to be there.
Give yourself plenty of time to get to the venue.