Most Important Point You have to Write:
Introduce yourself
Address the buyer need (Keep the proposal as descriptive and relevant as possible)
You need to put in writing to buyer’s interest.
Attempt to make your concept as persuasive as possible.
Talk to their interest,
Give them a purpose to hire right
Show your expertise with portfolio link(without contact information) and tell him/her to inbox for more details.
Write down your price and time(as sample 1) at the very bottom of the proposal. (Go for the lowest bid (because you are a new seller)
Conclusion: Just write “thanks”/“Looking forward to hear from you”