Check the material first
Read the fabric or kit guidance and identify the fibre, finish and any printed pattern. Some printed cloth is intended to be washed after stitching, while another fabric may need a gentler approach.
If no information is available, test a small offcut. Measure it before and after washing and check whether the print, colour and hand change.
Control the variables
Use the same water temperature, detergent and drying method that the finished object will receive. Avoid stretching the cloth while wet and let it dry flat if that matches the care plan.
Press lightly if needed, but do not create a new bias or stretch through aggressive ironing. Marking works best on a stable, relaxed surface.
Choose consistently across a project
If a patch, backing and garment will be washed together, consider their shrinkage as a group. Mismatched preparation can create puckering at the repair boundary.
Write down the decision with the project notes. The next panel or matching repair will be easier when you know whether the original cloth was stitched before or after washing.