Be familiar with the test item types and the administrative aspects of the examination, such as the total number of questions, how much time is allocated for the entire exam, how that time is distributed, and the like. In order to ensure the accuracy of the information, it is best to refer to the official site of the examinations board.
Please note that some examination boards allow the use of dictionaries (either monolingual or bilingual, or both) so it is worth checking whether or not this option is available.
The more information and insight you have regarding what content to expect on the test, the less likely you'll end up thinking, 'I wasn't prepared for that question'.
Test blueprints and practice tests are resources that will take you a long way toward becoming test-wise.
FAMILIARIZE YOURSELF WITH THE TESTS
Take a good look at the format of the test, look at the different question types, the instructions and all relevant information. Decide for yourself which exam is suitable for you.
IELTS General Training Practice Test
LanguageCert B2 Practice Test
TOEFL Practice Test
PTE General Level 3 Practice Test
Cambridge First Practice Test
Cambridge Advanced Practice Test
Euroexam B2 Practice Test
Euroexam C1 Practice Test