Dear Vinay,
You need to take training on Business Writing. Anyway I am trying to clear few of your doubts.
1. How to start with the letter, what should be the wording and points to be mentioned.
It depends on the type of the letter. Ask a question to yourself - why am I writing this letter? Am I instructing or informing or appreciating? am I apologising? Am I warning or reprimanding? Am I condoling? Am I writing product promotion letter? am I writing technical report?.
2. Can I elaborate on the subject matter in the very first para, if no then from where on.
No, you should not elaborate the subject matter in the very first para. Give reference of some policy, Govt regulation, rule, regulation, law etc. Otherwise mention just what has happened in the past tense.
3. Which are the mostly common word used especially in the beginning and at end of the letter.
It depends to whom you are writing and why are you writing the letter.
4. How should be the end of letter and kind of terminology used.
The phrases or terminology will differ if you are writing to superior or junior. Secondly, there are cultural differences too. You need to take into account that also.
I have given so many drafts in this forum, you could have done some search before raising this post. In the search box of this forum type "Draft Divekar" (without quotation marks) and you will get good number of examples. Two links are given below:
https://www.citehr.com/298986-how-do...ml#post1349509
https://www.citehr.com/411361-advise...ng-letter.html
Ok...
P.S.: - I conduct training on E-mail writing, Business writing skills etc. Guidance through forum is no substitute for the training. The earlier you take the training, the better
Dinesh V Divekar
Beware of false knowledge; it is more dangerous than ignorance.