In the closing paragraph of a formal letter, state what you would like the recipient to do, make a reference to a future event, or offer to help...
EXAMPLE: I look forward to hearing from you soon / I look forward to receiving your reply,
EXAMPLE: I look forward to receiving a full refund, (in a complaint letter)
AVOID: I look forward to hear ... <<< common grammatical error
AVOID: I look forward to receive ... <<< common grammatical error
EXAMPLE: I would like to know what you are going to do about this situation, (in a complaint letter)
EXAMPLE: I would like to thank you in advance for this information, (in an enquiry letter/requesting information)
EXAMPLE: If you require/Should you need further information, please do not hesitate to contact me/feel free to contact me.
Use 'Yours sincerely,' when writing to a named person.
Use 'Yours faithfully,' when using the 'Dear Sir/Madam' greeting.
Use the semi-formal 'Best regards,' or 'Kind regards,' if you wish the tone to be slightly less formal.
EXAMPLE: Dear Mr Jones, (...) Yours sincerely,
EXAMPLE: Dear Sir/Madam, (...) Yours faithfully,
EXAMPLE: Dear John, (...) Best regards, (respectful/professional)
EXAMPLE: Dear John, (...) Kind regards, (respectful/professional)
The closing always takes a comma.
Note that only the first word of the closing is capitalised, not the second word.
EXAMPLE: Yours sincerely,
EXAMPLE: Yours faithfully,
EXAMPLE: Best regards,
Learning English 'FCE Formal Letter' Retrieved from http://www.rubenvalero.com/english/content/fce-formal-letter-or-email
Oxford Living Dictionaries 'Choose the right greeting and sign off'. Retrieved from https://en.oxforddictionaries.com/writing-help/choose-the-right-greeting-and-sign-off
Oxford University Press 'Sample formal letter' ["PDF file] Retrieved from https://oup.useremarkable.com/production/images/uploads/3687/original/uk_sample_formal-letter.pdf