MTR/Metro From Tsuen Wan to Terminal 3 Shenzhen

Well, you may take MTR Tsuen Wan line to Prince Edward Station, and change to Kwun Tong Line to Kowloon Tong Station. Next, transfer to East Rail line to Lo Wu station. After crossing the Luohu Port to SZ, you may take Luobao Line to Hourui Station. Upon arrival, take bus line M416 to T3.

Or, you may take a direct bus to your destination from Tsuen Wan City Landmark, Tak Hoi Street. The bus fare is HKD 130. The buses are available from 8:00 to 18:30 at an interval of 30 minutes, and the duration is about 2.5 hours.

And you can find some malls on 3F and 4F inside the terminal building. :)