The main tourist season starts at Easter and runs until October; peak periods are in spring and autumn. Numerous outdoor festivals and concerts and the fact that Romans desert the city for the beaches and mountains, which means very light traffic and a less-crowded city centre, makes summer almost worth the heat. If you do visit in summer, try to hit the sights early, take a long lunch and a nap, and then head out again around 6:00 p.m. to take advantage of the cooler evening. Be aware some restaurants and shops close for the month of August. Winters are usually mild with few tourists and some fun events around Christmas time.
Rome's mild climate makes it visitable year-round; however, spring and autumn are without doubt the best times to visit, with generally sunny skies and mild temperatures (although late autumn, November, can be rainy). July and August are unpleasantly hot (many Romans desert the city in August so many businesses close at this time); from December to February there is briskly cold weather, although it's rarely grey and gloomy.
You are not expected to tip, but it's common (in bars, for example) to leave a small amount. If there is no service charge, the customer might consider leaving up to a 10% tip. Tipping taxi drivers is not common practice but you should tip the porter at higher-class hotels.
Also known as Fiumicino, Leonardo da Vinci is Rome's main airport, the other being Ciampino. Eurolines is the main bus company for servicing other European destinations, and there are regular train connections to all the major cities in Italy and Europe.