When you start sewing sashiko, it's easy to think that everything has to be perfect from the start. But many of the most common mistakes are easy to avoid.
A common mistake is to pull the thread too tight. This can cause the fabric to start to pucker and the stitches to lose their even rhythm.
Another is to try to make each stitch exactly the same length. In practice, it is often better to focus on the overall pattern.
Many beginners also sew one stitch at a time, which slows down the work. Picking up multiple stitches on the needle allows you to work more efficiently.
With a little practice, the technique quickly becomes more natural and the stitches find their own rhythm.