There must be at least a few other people out there who are nearly as interested in Pompeii's history and ruins as I am, and I did a lot of research on the site before I left home, so I thought I'd share it here for the benefit of others.
Planning in advance is critical to really get the most out of your time in Pompeii -- it's a huge site (most of a whole town), so walking from place to place inside takes a while. Also, directional signs and even signs with the (modern) street names are strikingly absent in many cases. Finally, only a few of the many excavated and restored houses and buildings are open on any given day.
If you have a real interest in Pompeii, it's easy to spend a full day at the site without running short of things to see. For a first time, it's good to plan a variety of places to visit, so you don't get bored (as if it's possible) just looking at house after house. However, if you MUST be there for only a half day visit, I would definitely suggest going in the morning, for two good reasons: 1) it will be cooler and less crowded in the peak summer season, and 2) some houses that are "open" on a particular day may only be open in the morning. If you arrive too late, you may find it closed, even though you were told it would be open all day (unfortunately learned by experience and also heard from others).
Here are some of the tips I picked up while researching the site:
1. Get a good map and become familiar with it. There are several on the Internet, but none of them is optimal -- and here's why. Pompeii is organized by Region (Regio; 9 in all), and then by Insula (Latin for "block") within each region. The roads throughout the site are frequently not signposted, but the Insula and Regio numbers are always indicated on the buildings. Once you acquaint yourself with this system, it is marvelously easy to find your way around the site. If you can't find a good map in advance, at least study some of the maps available on the Internet and mark off things that you want to see. At Pompeii, you can ask for a free map that has the Regio and Insula numbers marked on it.
2. Read at least one book about Pompeii before you go. (Robert Harris's novel is nice, but doesn't count.) I can recommend this one, which gives a lot of good info and visuals, and the price is very fair: http://www.amazon.com/Pompeii-White-...3759109&sr=8-1
3. Visit a good website, like the Google site, AD79 Eruption (https://sites.google.com/site/ad79eruption/), to get an idea of what you'll see onsite at Pompeii. Be prepared to do a little detective work. In nearly all the houses, the best frescoes (and often mosaics) were removed years ago, either by early "excavators" -- who often were working for wealthy private collectors -- or later by archaeologists to be kept safe in museums. However, there are still some houses in Pompeii where you can see stunning frescoes. Two in particular include the House of Menander (or Menandro, in Italian), which is only open on a rotating basis, and the Villa of the Mysteries, which is nearly always open but is a bit of a walk from the main site.
4. Make reservations in advance (at no charge) to visit two outstanding sites that are NOT open to the public without reservation and that cannot be reserved on the day of entry, the Suburban Baths and the House of the Prince of Naples. The site where this can be done is: http://www.arethusa.net/w2d3/v3/view...contenuto.html (the link should take you directly to the reservations page). The site is all in Italian, but you can use a translator if needed; it's pretty easy to figure out. Just remember when entering the date you wish to visit, that you must enter it in the European style (day/month/year). You must select a time for your visit. Note that the Suburban Baths is near the main entrance, so it might be a good idea to book your time to coincide with the time you plan to arrive or leave the site.
5. Arriving at Pompeii: Get there as early as you can. Your first stop should be the ticket line to get your ticket. Next, visit the small office to the left of the ticket line, where you can pick up the free Pompeii site map and a detailed "mini" guidebook full of information about the various houses. IMPORTANT: This is where you must also ask them to tell you which houses are open that day. Otherwise, there is no way to tell once you get inside the site, and you will waste a lot of time traipsing to houses that look good on paper, only to find them locked up tight when you get there. If you want to get a really good, detailed map, go into the bookstore to the right of the ticket line and look for it (multi-language) near the cashier. It does cost 10 euro but makes a dandy souvenir and is invaluable onsite for those who are truly interested.
6. Once you've done all of this and you know what houses are open, you can plot a course around the site. In addition to houses that are open, you should also plan to visit the Civic Forum (with its chilling view of Vesuvius), and the Forum Baths (just around the corner). In another area, you'll find the Triangular Forum, the Temple of Isis (very worth visiting if it is open), and the Large Theatre. Also visit the Amphitheatre. For fans of Robert Harris's Pompeii, it may be worthwhile to see the Castellum Acquae near the Vesuvian Gate (where you can also climb up on the ancient walls and take a nice photo overlooking the site). Many will want to visit at least one of the famous brothels (called Lupinare). Finally, as I already mentioned, consider walking to the Villa of the Mysteries (about 10 minutes outside the ancient gate, but still part of the site), the frescoes are stunning.
7. Set out on your trek. The streets can be hot and dusty. Fortunately, the water in most of the (ancient) fountains onsite is still running and is drinkable. There's a small restaurant near the Forum that crowded and expensive; best to bring something with you to eat, if possible. Bathrooms are also located here (and at the main gate).
8. There are periodic wooden one-room huts throughout the site that house the Pompeii guards. They can help you locate a house or area if you get lost, and it is sometimes necessary to find one to let you into a reserved house -- don't expect them to be waiting for you (except for the for-pay tours mentioned below).
9. If you are lucky enough to be visiting Pompeii on a Saturday or Sunday, there are two more "special" onsite options open to you. These are the House of Julius Polybius (featured in several specials on Pompeii that I've seen) and the House of the Chaste Lovers, which is right next door. These are only open for one tour daily, at 11:00 am (Chaste Lovers, or "Casti Amanti" in Italian), and noon (Julius Polybius), and only on the weekends. If you want to see them, you MUST make your reservation when you purchase your ticket at the main gate. You cannot do it in advance. There is an extra charge.
I hope this is helpful in planning a successful trip to Pompeii. After spending the better part of two days there, I have to say that I think it is a far richer site (in terms of the quality and variety of what you can see) than Herculaneum, but it is also more challenging because it is so big.
If you have any questions, feel free to ask.