I'm working as an Architect in a consultancy. Now I need to make an experience letter so that I can apply to other large consultancy. I don't know how to write a nice experience letter. Would you please help me?

Samjhana Dangol.
Just write as if you were speaking to him/her/them.
Please read the [url=http://www.englishforums.com/English/FormalGeneralBusinessLetterWriting-EnglishLanguage/Forum5.htm ] ANNOUNCEMENTS AND FAQS IN OUR LETTER-WRITING FORUM[/url], post your draft letter in that forum, and we will check if for you.