Make sure that you are happy with your witness statement. Remember that you will give this evidence on oath - if you are not satisfied that it is the truth or you feel uncomfortable, do not agree to it.
Make sure you are familiar with your statement - practice reading it out loud before the hearing.
Familiarise yourself with the bundle, particularly documents that you wrote or saw at the time.
Think about what may be asked of you in cross-examination and discuss these with your representative. How did you reach decisions? Are there any inconsistencies or areas of weakness? How will you answer questions on these?
Be polite and refer to the Employment Judge as Sir or Madam.