There is a small bus station near the Beihua Bridge. It takes 20-minutes walk to the Wuzhen East Town.
The easiest way is to take a day tour from Shanghai Gymnasium Stadium. Two tours per day: 7:50am and 8:50am, return to Shanghai at 16:30. Y145 includes transportation, entrance fees, and Chinese tour guide only.
Shanghai South Bus Station
Address: No.666, Shilong Road, Xuhui District, Shanghai
Buses leave and return at this bus station 4 shifts per day. (2 hours)
Hangzhou Passenger Transport Central Station (杭州客运中心站)
(refer to my Hangzhou Transportation Tip)
Buses leave and return at this bus station 16 shifts per day. (1 hour 30 minutes)
If you travel like Hangzhou --> Wuzhen --> Shanghai, you can only buy the Wuzhen-->Shanghai bus ticket at Wuzhen bus-stop. Due to limited buses going to Shanghai each day, you can alternatively take a bus to Jiaxing, a bigger town near Wuzhen (Y8, 1 hour). Then, from Jiaxing bus station to Shanghai (Y30, 2 hours). Jiaxing West Bus Station is bigger with more routes to Shanghai.
Bus Stop Name in Chinese: 嘉兴汽车西站
Although there are cheap public buses (these leave from the long-distance bus station), in my view they are not frequent enough to make it a viable option, especially if you are short on time. The most efficient solution for me was to hire a car with the driver, and combine the visit to Wuzhen with another of the nearby water towns. In order to overcome the language barrier - for those for whom it exists, like me! - best was to let the concierge hotel negotiate with the driver. They can also help plan the trips around water towns more efficiently - i.e., tell you which two are best visited on the same day. I had a trip of 6 water towns arranged like that over 3 days.
You can also take an organised tour.
From Shanghai, it's about 2-hours' drive along the Huhang Highway (from Shanghai to Hangzhou), which you leave at Tudian exit. Wuzhen is clearly signposted. Despite navigation not being difficuly at all, best to hire a driver if you are not familiar with Chinese traffic as a driver!
If you walk from the ticket offices to the main road and turn left on the corner on the opposite side of the road is an unmarked bus stop. You can catch a bus to Tongxian (about 30mins CYN6). There is a huge bus station there and you can travel on to anywhere else you need to go even late at night.