I found that if it's for a well known business, searching online for things like "(business name) interview questions" can allow you to find some forums with people telling you how the interview is structured and what kind of questions/tasks they will ask of you. You may feel less anxious being able to anticipate what they will want from you before you walk in and you can think of some answers to stock questions beforehand.
Also, do be yourself. We anxious people respond in different ways to stressful social situations - for example, in group interviews they may make you do some random group activity like building a tower, and if you're not a natural "leader" in a group, don't force yourself to be. You may instead be more quiet but a good listener and instruction follower. These traits are also good in the eyes of employers.
Finally, when it comes to speaking to others in the group, just have some stock questions in your head so you will never be in silence. Things like "where are you from?" and questions about the job is fine, everyone is nervous and won't be expecting amazing conversation.