On sheet metal parts, we often have to consider both grain direction and "good side." As a rule, I orient grain in the X direction of the flat pattern and the good side is face as "front." However, it is easy to make a mistake especially as the parts become more complex as it is more natural to mark these two attributes at the folded part level. So instead, I emboss an arrow on the folded part and then appropriately change the flat pattern until i see the arrow and have pointing in the correct grain direction. Then I remove or suppress the embossed arrow because I don't want it going to our CAM software.
It would be great for Inventor to allow you to set a grain direction and "good side" from the folded part that would translate to the flat pattern.