What is the best way to travel from nanjing station to yangzhou?

I wonder if you will arrive at the South Railway Station. If so, you are suggested to take local subway line 1 or line 3 to the Main Railway Station, where you can take a bullet train to Yangzhou and it takes around 50min. And there are many direct buses at Yangzhou West Bus Station to Suzhou, which takes about 3h.

Thank you.
Do you need to book tickets for the bus in advance or is one day before enough?

Would it be quicker to go back to NJ and from there to suzhou?
Or is the bus ride very special?

Actually, you can buy the bus ticket on the spot upon arrival. You needn't book it in advance.
Well, you can take a bullet train back to NJ from Yangzhou (about 50 minutes). Then, take a bullet train to Suzhou (1 to 1.5 hours). It takes less time. But taking the direct bus involves no transfers. You can choose the way you like! :)