Hexedecimal editing

I have spent the past two or three years trying to learn to hex edit. I am able to change text in the program and get rid of dialogue boxes or menues if I am lucky. However, my learning is very slow, because I am teaching myself, and I cannot findany book on it. Can somebody tell exactly how to hex edit, or can you tell me where I can a book that will teach me? I want to learn to be able to do serious hex editing, not just text editing or deleting a couple lines that from a dialogue box.