Hi Mairip
Welcome and congratulations on taking the plunge and booking your first JY trip!. I did the Pompeii tour in September last year and had a fabulous time. If you use the search facility at the top of the message board using 'Pompeii' you'll find reviews from myself and other travellers and loads of tips and suggestions. We were very lucky in my week and had beautiful weather (almost too hot at times) but I know the group the following week had a lot of rain. Luck of the draw really.
My top tips would be:
Take very comfortable walking shoes, do the Herculaneum excursion - in my view, even better than Pompeii and, thanks to the local restaurants and gellatorias, don't weigh yourself when you get home:D
Happy to help if you have any questions
All the best
Mandy