Before calling on your first witness, it is important to discuss sensible guidelines to answer questions.  For some, it could be their first time being on the witness stand, so it doesn't hurt to take the time to prepare your witness.

The Continuing Education of the Bar - California compiled a list of 21 things to tell your witness before answering questions.

1. Tell the truth.
2. Don't be afraid of the lawyers.
3. Relax; don't lose your temper.
4. Speak slowly and clearly (most of us speak faster than we realize).
5. Always be sure of the question before answering; if you're unsure of the question, ask for a repeat or rephrasing.

Read full list here