Telephone the companys and ask who is the facilities manager.Once you have the name send them your letter saying what service you can provide for them.Dont put the price in you have to get them interested first. Once you have done this call them back after a week and ask if they received and if so woud they be interested in your service. Alot of companys will have someone allready and all the real big companys will use one company for all thier sites. if in doubt go around your local area and look to see which buildings are dirty then you can asume they dont have a window cleaner. Also you will need insurance,risk assesments,method statements etc etc