During my visit to the Amalfi coast and Naples I took a 60 minute train ride from Naples to Pompeii for a day trip. It was about $3.50 (€3) each way. If visiting from Naples get on the Naples–Sorrento line and look out for the Pompei Scavi-Villa Misteri stop. From there its a short walk through a few stalls, restaurants and shops until you see the ticket booth.
Admission for Pompeii was $15 (€13). If you also want to see Herculaneum you can get the 5 site 3 day pass for $25 (€22). It takes about 3-4 hours to see each so you may want to break them up into separate days if the weather is very hot.
I recommend the self guided audio tour or hiring a private guide to learn about the history and culture of the civilization that was discovered in excavation of Pompeii. I found the group tour guide hard to understand at times and everyone in the group seemed more involved with picture taking than listening, which I found distracting.
Be sure to check out the Forum, Coliseum and Garden of the Fugitives.
As you can see the streets are made of smooth rocks so it’s hard to walk the streets of Pompeii and you’ll need to be careful and watch where you step. I saw a lot of people in heels and flip flops suffering from achy feet so be sure to where good walking shoes.
I also used an app called Pompeii Touch to see what the sections looked like before and after the eruption. It’s nice and really fills in the gaps for you.
If you prefer to do more of a pre-arranged guided tour with a pick up from your hotel or vacation rental check Viator. They offer tour options to Pompeii as well as other day trip alternative for visitors to Naples and Sorrento like visiting Mt. Vesuvius (pictured below), wine tours and cooking classes.