Question

how to use phrases in letterwriting. Please give some hints in various letters

Answer 1

use of phrases is apropiate in informal letters more than formal

Answer 2

Some phrases are:
Starting your letter (Paragraph 1)

Thanks for your letter. 
Lovely to hear from you. 
How are you? 
How are things? 
Hope you're well.

Commenting on something (Paragraph 1)

I'm sorry to hear/learn ... 
I'm so pleased to hear ... 
It's great to hear ... 
What wonderful news about ...

Moving the topic on (Paragraph 2)

Anyway, the reason I'm writing ... 
I thought I'd write to tell/ask you 
Anyway, I was wondering ...

Ending your letter (Paragraph 3)

Well, that's all for now 
Write back soon 
Looking forward to hearing from you again 
All the best 
Best wishes 
See you soon 
Take care 
Yours 
Love 
Lots of love