Unlike some other countries Italy does not keep its civil records in one central location, all records are kept in the town where the act took place, whether it is birth, marriage or death. In a country prone to earthquakes, and in the past, wars, not all records have survived. Fire, floods, tsunami have all taken their toll. However the towns and churches for the most part have managed to keep their records in one form or another.
For Italian immigrants to the USA it will be easier to find the town of origin. Ship manifests at Ellis Island usually provide the town of birth or last residence. Prior to 1900 this information is often omitted so you will need to access naturalization records which usually give the town of birth. Obituaries can often give a clue if all else fails.
Those searching emigrants to the UK will find this a more difficult task. The 1911 census asked for town of birth so this should be your first stop. Other census years rarely give more than the country of birth so you will need to be more creative.
First step should be to check the distribution of the surname via on-line sites for this purpose. http://www.italygen.com/italiansurnames/italian-surnames-map.html. These maps are created from today’s white pages of the telephone book so may not accurately reflect the distribution in the year your ancestor emigrated. Except for very common surnames it should tell you whether to look in the north or South of Italy. http://italia.indettaglio.it/eng/cognomi/cognomi.html will help narrow things down when you have an idea of the province. You can check the white pages yourself at http://www.paginebianche.it. This time look for the first name in conjunction with the surname. Remember to change the final vowel from ‘a’ to ‘e’ or ‘I’ to ‘o’ the final letter often got changed on arrival in another country. Your ancestors were probably illiterate so how they pronounced their name could change how it was written. Double the consonants if you aren’t getting many hits or change the vowel, Palazzi, Palazzo, Paluzzo, Paluzzi. In the Italian language every letter is pronounced. Ask an Italian speaking friend to listen to the pronunciation as your Grandfather said it and write down the name as it ‘sounds’. http://genealogy.familyeducation.com/browse/origin/italian this site will help with variations of spelling.
Some first names are very specific to different parts of Italy. For example Restituta is found predominantly in Sora (FR) and areas where Santa Restituta is the Patron Saint. Gennaro will almost certainly be from around Naples or have Naples ancestors. Diego is most common in North Italy. Roman names will be found in the Rome area. If you are struggling with spelling of first names this site might help http://www.italianames.com/italian-baby-names.php
Some people emigrated to escape the stigma of illegitimacy. A new immigrant rarely needed to indicate the name of his/her father so their illegitimacy was not so obvious.
Surnames were invented for these abandoned children and were surnames not found in the town where they lived. Italian documents always name the father and if you don’t have one the document reads N.N. or ‘genitori ignoti’ (unknown parents). Common examples are Trovatello (found) Benvenuto (welcome). There were so many ‘Esposito’ in Naples at one point the surname had to be taken from the list and others invented. These invented surnames will show sparsely or not at all on surname distribution maps or in the telephone book. Or they will show in numerous areas as indicated on this table.

Latin or Italian Meaning in English
Della Casagrande “Of the Ospizio” (of the Hospital or Hospice)
De Domo Magna “Of the Ospizio” (of the Hospital or Hospice)
Innocenti “Innocent One”
Della Scala Name assigned by foundling home in Sienna
Projetti Name assigned by foundling home in Rome
Esposito “Abandoned”
Degli Esposti “Abandoned”
Ospizio Foundling Home
Incogniti “Unknown”
Circoncisi “Circumcised”
Palma Surname given to child born or abandoned on Palm Sunday

Check the census records for other emigrants in the same town to see where they are from. Emigrants tended to stick together, they spoke the same dialect, ate the same kind of food and if they were looking for a wife, usually chose one from the same area in Italy that they were from.
You might also want to request records for known siblings of your ancestor. They may have given the town of origin on their naturalization paperwork or on the ship manifest.
Think about the foods Grandma used to cook. If she cooked with oil rather than butter or lard, the family are probably from central or South Italy. Butter was used almost exclusively by those living in the North near France, Germany and Croatia. Tomato-based sauces were more popular in the centre and South where the climate is warmer, while white sauces and béchamel were more common in the North. Polenta and corn based dishes are also a north Italy specialty while pasta was a staple in the South.
The Saints are very important to Italians. Did Grandma or Grandpa call on one in particular? San Gelardo, San Gennaro (Naples), Santa Filomena. Italian town websites will often list the town’s patron Saint. My Grandmother wasn’t Italian (or even Catholic) but she constantly called on ‘St. James Church’ I was amazed to learn from the census that she lived in St. James’ Parish as a child.
Finding the town of origin or even the town where a death or marriage took place is essential when searching for Italian ancestry. Once you have it, the road will become much easier to travel as Italian records are interlocking, leading the researcher in a straight line back to the next.