As you can see, you've gotten great advice so far. Let me add one more useful tool to help make the adjustment to composing upside down and backward a little easier...the viewing card! If you're not already familiar with it, it's simply a cardboard rectangle with a 4x5 rectangle hole cut into it. Close one eye to emulate the non-stereoscopic view the camera lens makes and squint a bit to help see the values apart from the reality of whatever the subject is you're considering and compose that way. When you are happy with what you've chosen, it isn't a big deal to adjust the gg to emulate what you've decided on. My dad told me when I was young to never compose in the camera (and he was referring to a view camera at that time). I'm not sure his 'absolute' rule is always true, but it's a pretty good one to keep in your kit. Good luck!