I had a life long wish to visit Pompeii. In September 2013 I finally got there. I took my sister who had never had a real holiday and she was just as excited. We booked a room in the Hotel Una which is in the centre of Naples. Loved it. Reasonable prices and great breakfast on the rooftop every morning. We went native on the food buying from small local places, usually carrying out and eating in the sun. This saved a fair bit of money as there is a tax if you eat inside. Pompeii is not far from Naples, a train gets you there in 30-40 minutes and it stops at its own dedicated station. We arrived to a throng of people queuing up and it took ages to get in. Once in it was very difficult to navigate to the interesting bits. There are no sign post to help you get around. It can be exhausting. We did have a map, but it's too easy to become disorientated. It is also very commercial. For instance they advertise bus trips to the top of Vesuvius for 12 euros. We later spoke to a couple of Canadians who said they took this trip and were really angry to find that once they got to the top they had to pay another 12 euros for the tour. We stayed at Pompeii for an hour and half then decided we had had enough of wandering aimlessly in the heat and getting trapped between endless large loud tour groups. We decided to go get the train back to Herculaneum instead, which you pass on the way to Pompeii (about half-way). What a contrast. It is fabulous. Smaller but with so much more to see. It's what Pompeii would have looked like it it had not been destroyed to the degree it was. It is compact and so interesting. We spent several hours there. As you get off the train at Ercolano head on down the main street and you'll see the large archway to the site straight ahead of you. About a 5 minute amble. You get a fantastic view of it as you take the purpose built long walkway from the archway to the ticket office. This preview which just whets the appetite. It is not as busy as Pompeii which just added to our experience.
My advice is give Pompeii a miss if you can and do Herculaneum. Use the time you might have spent at Pompeii visiting one of the many other treasures that Naples has to offer.
Wherever you go take a bottle of water. Buy these at small local shops where you'll pay 1euro a bottle rather than 5euros at the tourist traps. Top up at the endless fountains found on the streets etc flowing with fresh ice cold delicious water.
I finish with a warning. DO NOT get involved with taxi drivers who approach you inside the railway station. They will deceive you and charge a lot for it. We know this first hand and would hate to see anyone else have this mar their holiday. Go to the taxi rank outside the train station if you need to get a taxi anywhere.