Write out the questions you believe are important to ask beforehand. Then you will not forget them. List points you want to make so you can check them off as you make them.
You can practice with your witnesses ahead of time. Stress to them that they must tell the truth.
In the courtroom, you start by asking your witness their name and address. If your witness is a counselor or other professional, ask what their job is, what their educational degrees are, and how long they have been doing their job. Then ask specific questions about the information they have about your case.
The other side will question their own witnesses first. The judge will let you ask them your own questions ("cross-examine" them). Never ask a question you don't know the answer to. The answer may hurt your case more than help you.
You can choose not to cross-examine a witness if you think they will just repeat their direct testimony. It might be better to wait and contradict their testimony, either with your own testimony or with the testimony of one of your witnesses.