Or do you usually wait for a melody idea or something to come to you (wherever and whenever that may be), and then start writing off of that idea?
i am very diligent about capturing ideas whenever they fall on me, because this is just how ideas tend to occur. so a large amount of starting points from songs actually come from those ideas that fall on me at an unexpected time and place. it is very important to meticulously catch all these ideas as they fall on you. generating ideas from a blank desk can be done but it is only part of the picture