You must have completed knowledge as to what the event is about. If it is an inaugural event, you must know the designations of the people you will be introducing. Introducing the company CEO as the Finance Manager will seem ridiculous.
Introducing people as they come onstage for a word with the audience is an emcee’s most important job. You need to know which people to introduce and when to introduce them during the event. Again taking the example of an inauguration ceremony, there is no way you can skip introducing the CEO of the company. Similarly, you can not introduce the chief guest at the very start.
In order to introduce people in the right order, you need to know the sequence of events. It will be embarrassing if you called out the CEO’s name if it was the part where the audience was supposed to be educated about how the product being launched would work.
Pronouncing names the right way is very important. If you will be introducing foreigners during the event, make sure you rehearse their names to get the pronunciation right. Consider writing all the foreign names phonetically and rehearse the names in advance.
Remember as an emcee you are just required to introduce people, not to give a speech about their biography. When introducing guests, use a limited number of words and avoid going into details about the guest you are introducing even if you know the person well. During your introductory speech, you do not want to say anything embarrassing that may offend the guest being introduced.