The interview is conducted in English and you need to be perfect in that. Next, make sure you have all of your documents ready whenever they ask you (transcript, a bank statement, your acceptance stuff, matric docs etc). Finally, get ready to give satisfying answers for their questions. (They will ask you like why do you want to study in this uni? Tell us what you know about this uni? What will you study there? Why do you want to study that etc. You can search mostly asked questions on Google and download it.)