Set the main axes
Find the centre or a clear edge and mark the first horizontal and vertical references. Check them against the grain and the object before adding every repeat.
Use a ruler or gauge that matches the scale you want. A small error repeated across a wide cloth can become a visible drift at the final border.
Choose a temporary mark
Test the marker on an offcut and follow the removal instructions. The line must remain visible long enough to stitch but should not become a permanent part of the finished surface.
Use light pressure and avoid drawing over the same line repeatedly. Heavy marks can spread into the weave or leave an impression after washing.
Check the grid before stitching
Measure a few cells across the field and compare the opposite edges. Correct the reference while the cloth is still unstitched and flat.
Leave a clear margin around seams, hems and patch edges. The grid should guide the motif, not force stitches into places where the object needs to move or fold.