Hi Mayflower
Welcome! You'd picked a great trip for your first tour - I did it in September 2015 and we all had a super time.
If you put 'Pompeii' into the search box on the top right of the page, you'll find loads of reviews, hints and tips from people like me who have done the tour already.
My number one recommendation, apart from sunscreen and a hat, is to make sure you have really comfy walking shoes (closed toes) because the pavements (especially at the ruins) are extremely high and uneven. Watch your step and have a wonderful time!
All the best
Mandy