Dear Sir,
We are very pleased we have a so good customer as you。We have a good cooperation in the last year,and we hope we will have some good business in the new year。
  
Best wishes to you and your family。Happy New Year!
Best Regards,
your name
另外这有几句祝福语，可以选用
I give you endless brand-new good wishes。
   Please accept them as a new
remembrance of our lasting friendship。
给你我无尽的新的祝福，让它们成为我们永恒友谊的新的纪念。
Season's greetings and sincere wishes for a bright and happy New Year!
献上节日的问候与祝福,愿你拥有一个充满生机和欢乐的新年。
  
Please accept our wishes for you and yours for a happy New Year。
请接受我们对你及你全家的美好祝福，祝你们新年快乐。
Allow me to congratulate you on the arrival of the New Year and to extend to
you all my best wishes for your perfect health and lasting prosperity。
  
恭贺新禧，祝身体健康、事业发达。
Please accept my season's greetings。
请接受我节日的祝贺。
。