Sichuan is a relatively large province, with very large differences in climate. Therefore, the best time to see and travel different scenic spots in Sichuan is often not the same. You should decide the destinations you want to visit first.
Typically April - May, and September - October, is tend to be the time with the beautiful scenery in Sichuan. Especially in the fall season, it is often the most beautiful time throughout the year. In addition, July and August are peak season for tourism in Sichuan, mainly in Sichuan-Tibet line and Ruoergai grasslands. There will be many people at this time, and the price is relatively expensive.
The native language of most of Sichuan is a variant of Mandarin (Southwest), which differs from standard Mandarin of the north-east significantly in pronunciation, and use of slang which are unique to the area. Nevertheless, native speakers of Mandarin will be able to understand the local dialect albeit with some difficulty. Tibetan is still the mother tongue in most of the highland west, but the region becoming more and more Sinofied. There is a moderate amount of bi-lingual signage in the area. Therefore, many young people in the western regions are bi-lingual in both Tibetan and Mandarin or just speak Mandarin. Qiangic, native to the Qiang minority group, also native to Sichuan, can also be found in isolated parts of western Sichuan. The vast majority of signage is always in Mandarin Chinese characters throughout the province regardless of the ethnic majority in the given area albeit you will see some signage in Tibetan indic script. Many young people in Sichuan's larger cities speak some English.
Chengdu, the capital of Sichuan has a fairly large modern airport with domestic connections to many cities all over China and also some international connections. Internationally you can fly from Europe (KLM), the United States, Singapore, Japan, Korea and Hong Kong, and many people arrive and depart using the very good air services available.
China has an extensive railway network and Chengdu is well connected to many cities by rail. One recent innovation is a fast train between Chongqing and Chengdu. Chongqing is a very large city which was part of Sichuan until 1997 but now is an independent municipality. Many trains shuttle forth every day between Chongqing and Chengdu. Not so long ago, the journey took anywhere between 4 and 8 hours depending on stops. Now a fast train (up to 200 kms per hour) run several times a day between the two.
Another option are buses. Buses run between Chongqing and Chengdu taking about 4 hours. However, bus travel seems to be less reliable than trains because of road works that are often occurring.
There are also several options of traveling within Sichuan. Many popular tourist destinations such as Leshan and Jiuzhaigou National Park are serviced by buses. The network is quite extensive and the highways are good. Buses also seem to mostly run on time.
Air travel is available within Sichuan if you want to go to Jiuzhaigou National Park which is over 300 kms from Chengdu.
Sichuan cuisine is well-known worldwide, including dishes like Kung Pao Chicken (宮保雞丁) and Twice Cooked Pork (回鍋肉). It is also famously spicy, with liberal use of chilies and the indigenous Sichuan pepper (花椒; huājiāo).
One of the other specialty of the area is the Hot Pot (火锅; Huoguo, cheap but extremely spicy.
The province of Sichuan suffered a catastrophic earthquake on May 12, 2008 centered on Wenchuan County, about 100km north of Chengdu city. Many cities were nearly completely destroyed and over 80,000 people are dead or missing with hundreds of thousands more injured or homeless. Government response was fast, but reconstruction will take years.
Many of West Sichuan's main attractions are located at altitudes above 3,000 meters and thus altitude sickness is a threat. Make sure to monitor your own health and take it easy for a day or two if moving from the low lands to higher elevations.
To help combat this sickness, many local Chinese eat medicine known as Hong Jing Tian. These are red capsules that the soldiers of the People's Liberation Army use to help them quickly adjust to altitude conditions in the Western Chinese provinces. Local tour companies will have a ready supply of this medicine if you ask.
There is also tension in Western Sichuan between the Chinese government and the mainly Tibetan people there and travel restrictions may apply to this area. See the warnings under Tibet.