Decide which way is up
A fabric with trees, lettering or a strong one-way motif can look quite different when turned sideways. Before planning cuts, decide how you want it to face in the finished quilt. Mark that direction in your notes, especially if the piece will be cut into smaller units and rearranged.
Print direction and grain are different clues
The warp runs along the length of the fabric, parallel to the selvages. The crosswise grain runs from selvage to selvage. A printed motif doesn't always tell you which grain is which. Check both the fabric edges and the design instead of relying on the illustration alone.
Check before allowing rotation
In the backing calculator, keeping the warp vertical prevents a horizontal panel plan unless you allow rotation. That permission means you accept turning the fabric in the quilt. Only choose it after checking the actual print. A smaller yardage figure isn't useful if the backing ends up facing the wrong way.
Make one unit and turn it in the layout
Strip-pieced blocks can rotate the print again when crosscut units are arranged. Place a sample unit where it will sit in the block before cutting the rest. QuiltMargins can calculate the sizes you enter, but it can't inspect your fabric or decide how a motif should appear.