It's not scary, just keep you cool. My two tips are only answer direct questions - they like to place works in you mouth gently by phrasing questions as statements. If this happens just ask the beak "I'm sorry, I don't understand the question".
My other advice is that if they imply you are lying ask the Magistrate/Judge for permission to step down to seek legal advice on the basis that you're being accused of perjury, which is a serious offence.
Barristers are nothing special. They're basically solicitors that generally specialise in court work, nothing more. They will sometimes (not always, it ain't like tv) try it on and it's up to the prosecution to let the beak know that out of line before they'll act. Now, prosecution solicitors are often crap - if they were halfway decent they'd be in private practice earning upwards of £180 and hour for their services. Because they're often useless you may as a witness need to speak as I've described above to gently let the bench know that the defence is being a bit fresh, and they almost certainly will chop them off at the knees. These power dressing, arsey and confrontational defence solicitors you see on tv are the exception and if your one starts to push his luck he will get slapped back into line but only so long as you let it be known he's being a twonk.
You don't need to take notes in. If you can't remember something just ask the bench if you can refer to your original statement to refresh your memory.
The experience can be intimidating even when it goes smoothly. The court surroundings aren't soft and cuddly and you'll get to mix with all sort of ne'er do wells in the public areas. But keep cool, think before you speak, and you'll be fine. Good luck.
and may the driver get everything he deserves to get!
