Just to be clear, since I couldn't really tell from the OP.
Are you writing about photography, or is it more photo journalistic in nature, where you tell a story (not necessarily photography related), through images?
If the former, I would start with a aspect of photography that appeals to you (a specific style or area of the trade for example), and write about that.
You could choose a photo, that you really like (one of yours) and write about the process behind it.
If your approach is more journalistic, you basically just find anything that you wan't to tell poeple about. Start with some good strong images, that tell the story and bind them together with words.