1. Meet with and speak to your attorney as often as possible prior to testifying.
He or she will need to over the facts of your case as well as familiarize you with how the proceeding will work. During your time with your lawyer he/she will also prepare you for the types of questions you may be asked as well as get a feel for what kind of a witness you will make. He will tell you to remain calm, articulate clearly and get your fact straight before answering questions.

2. Always tell the truth
This is a lesson many of us were taught in youth and it generally serves us well (especially when the penalty for lying may mean the loss of your case). When testifying before a judicial body not only can lying come back and bite you on the butt, it can hurt your attorney as well. Lawyers are ethically bound (in theory) to disassociate themselves with a client whom they know is giving false testimony.

3. Don't try to outwit the opposing counsel.
If the person interrogating you is an attorney, then he or she will be an expert in questioning people. Don't play a mind game with someone who has studied years in the art of polemics. Attorneys are trained to find and exploit testimony which may indicate that a witness is being untruthful. You best bet is to stick to what you know to be the facts of your case and not try to verbally joust with the questioner.

4. Don't guess at what you do not know.
Judicial bodies are designed to find the truth. To this end, wild speculation only hurts your case. Answer "you don't know" if you don't know or that you do not remember if you don't remember. Bear in mind, you cannot contradict yourself if you initially don't remember something and then recall that information when asked again at a later date. An affirmative or negative response always leaves a person subject to contradicting himself later. (This is only of course if you don't tell the truth which again you always should.)

5. Listen to and answer only the question you are being asked.
Answer only the question being asked of you. For example: If someone asked you if you knew what time it is and you looked at your watch and said "noon." That answer would be wrong. A correct answer would be "yes" or "no." In this example, you would have been answering the question, "What time is it or what time do you have?" Be precise in your responses and listen.

6. Pause before answering questions.

When you are being questioned don't be rushed to answer questions asked by the opposition. Take your time responding. This gives you time to think and time for your attorney to raise objections to questions raised by the questioner. The questioner may change the tone or pace of his answers; don't let them make you change yours. Questions asked in a rapid fire and aggressive manner are designed to throw you off. If you answer in a casual, deliberative manner it might also help to break the momentum the questioner may have gained.