I give evidence a lot for work at Crown Court. The court staff will be really nice and put you at ease, always ask of you’re unsure.
If at Crown- the biggest tip I got is always speak to the jury, not the barrister asking questions. I know it seems weird that you don’t face the person asking the question, but the barrister is there to ask questions to paint a picture to the jury so always direct your answer at them.
If the judge asks you a question though make sure you answer them facing them! And call them Your Honour (Judges are really up their own arseholes and stupid like that).
Take some food with you too as very few courts have canteens these days and you could be there all day without being called.
You’ll be fine 🙂