At the end you should sign off with "sincerely yours" or any other related salutation.These are some simple examples you can use to create your own letters of intent. However you need to take special care and avoid making mistakes and errors. Make sure you use the right format and pattern.
I use LOI's a lot when I am trying to buy a property for much less than what the seller says they want, more flexible terms than the seller says they want OR if I am unfamiliar with the property and area I will use the LOI to start the negotiating process while I do my due diligence work in the background. Remember, most of the time an LOI is not a formal offer but mainly a point of understanding between you and the seller.