Which trains to book ahead of time?

Any of the "high speed" trains, you will get a slight discount if you book early. Most folks will not suggest booking early for a train on the same day you arrive into the country, because you are at the mercy of airlines, airports, and customs. So you may be late.

We ended up booking early on the fast trains from Milan to Venice and Rome to Naples and it saved some money.

I think you can book 90 days or 120 days out...I'm not sure.

lily,

You'll likely be using the Freccia high speed trains on all the routes you mentioned. You could also travel on the competing Italo high speed trains as they also service the routes you'll be travelling (although they may use a different station in Rome so keep that in mind).

You can save money with advance purchase Super Economy or Economy tickets, provided they're not all sold out. Purchasing WELL in advance is the best practice and there may still be a few discounted tickets available for September. One important point to note is that these tickets have compulsory seat reservations which are specific to train, date and departure time, so the tickets you buy will only be valid for the ONE train listed on the ticket. If you're willing to commit to a specific departure, that's not a problem. Also, with the Super Economy tickets, these are non refundable and non changeable once purchased.

In Italy all trains except Regionale trains require a reservation. You can make that reservation five minutes before you get on the train or five week. The ONLY reason to make advance reservations on line is to take advantage of any discount that could be available. The super economy fare in Italy can be very, very cheap but it is no change, no refund. The economy fare is decent and allows for one change with the payment of the higher fare. The base fare is available all the time. If willing to commit to a fix schedule then look at the super economy and economy fares.

The cheapest way (and of course, slowest) is the Regionale trains but they are slow. Buy a ticket at the station, validate date, and get on. No reserved seats.

PS All posting about the same time. On the discounts - It all depends on the time of day, train, etc. But base fare can be 60 Euro or more to Venice with a super economy tickets being as low as 9 Euro. And economy around 20 Euro. More than a slight discount. Discounts can be substantial.

If you are looking to save money, buy tickets as far in advance as possible. You have 2 choices...Trenitalia.com or italotreno.com. Both have high speed trains while italo treno has newer trains. If you buy 120 days ahead, you can usually get super economy fares on trenitalia for all of your trips. Italo treno will offer similar fares. Check both for schedules and prices and choose your best option. The cheapest fares will lock you into a specific train.

Make sure you know which stations you are traveling to/from. For Roma, you can travel to/from Termini or Tiburtina. In Florence (Firenze) you will probably wan to use Santa Maria Novella. For Venice (Venezia), use Santa Lucia.

Sometimes Trenitalia has 2-for-1 sales on weekends, but the super-economy tickets may still be cheaper. You can buy up to 120 days out.