Like Les, my first consideration is the light on the subject. If the light is not right, I'm not going to waste the film. I do use a composing card made of 12x12 plastic with a 4x5 hole cut in it. I use it for both 4x5 and 8x10. I use a big piece of plastic because I like to be able to really isolate the window from other information outside the frame. If you like to shoot subjects that require you to isolate forms and details for abstracts from a larger subject this is ideal.
Depending on the subject matter I will explore the object or the area. If it something that is static like a structure that I have frequent access to, I may make exposures under different light. Here in the Plains the light of winter is drastically different then the light of summer.