At the end you should sign off with "sincerely yours" or any other related salutation. If you are writing a letter of intent for graduate school then it would have a different content. First of all letter of intent would start with your name, address, contact number and email address. After you have mentioned the date, you should then add a salutation like "Dear Sir/Mam".
In sum, the rationale underlying the Seller's demand for LOI, can essentially be summed up as follows: 1) That giving an LOI to a seller by a prospective buyer, is an indication that the buyer is "serious" and willing to purchase; 2) That use of the LOI is the usual way of initiating a purchasing proposal by a buyer, and is the right and proper way to go; and 3) That there is nothing for anyone in the deal to lose by a prospective buyer signing an LOI.