Generally, a classic Suzhou tour takes about 1~2 days. Visiting Suzhou, you can't miss elegant Suzhou gardens, like Humble Administrator's Garden, Lingering Garden, Master of the Nets Garden, etc. You can choose one or two of them for a great garden delight. Other must-be-visited sights in Suzhou City include Suzhou No.1 Silk Factory from which you can watch the process of silk making from silkworms to elegant products, Tiger Hill which is known as the first sight in Suzhou, Suzhou Museum which is designed by I. M. Pei and Suzhou's old canalside roads (like Pingjiang Road and Shantang Street), etc. If you like Jiangnan watertowns, you can visit Tongli, Zhouzhuang or Luzhi to have a wonderful time.
In fact, most people travel Suzhou with Shanghai - the best gateway city to Suzhou, and Hangzhou which has long been on a par with Suzhou since ancient times. Generally, it needs 2~3 days enjoying Shanghai's highlights and another 2~3 days appreciating the poetic beauty in Hangzhou.
If you want to explore more about Yangtze River Delta, you can travel to Nanjing for its profound historical and cultural charm and unique city dynamism; Huangshan (Yellow Mountain) for its mystical granite peaks, ancient pines, and sea of clouds; Wuxi for its breathtaking Taihu Lake scenery, sacred Buddhist land with 88-meter-tall bronze Shakyamuni Buddha, etc.