One of the most important things you can build into these documents is a clause that allows you to perform proper "due diligence" on the property. Basically you want to make sure that you have time to review all of the necessary financial information, management documents, and fully inspect the property itself BEFORE you finalize the purchase of the property. If things are not what they appear to be on the surface, it is better to find out now _ before you own the property than 6 months down the road.
LOIs are beneficial to both the buyer and seller. The fundamental goal of the LOI is to confirm that a 'meeting of the minds' has been reached prior to both parties making the large investments of time, energy, and expense required to execute a Definitive Purchase Agreement (DPA), aka Asset Purchase Agreement (APA).