Make the grid reliable
Use a cloth and marking method that keep the grid visible long enough to complete the stitching. Check the spacing on a small section before transferring a large field.
Count from a clear edge or centre line and protect the first few rows from drifting. One skipped interval can change the alignment of the pattern that emerges later.
Work in an order you can repeat
Many hitomezashi patterns are easier to manage when one direction is worked consistently before the crossing direction. Follow the pattern instructions if they specify an order, and keep the thread relaxed at every turn.
Use a sample to find a comfortable group size. Dense single stitches often need more frequent resets than long running lines.
Keep the cloth flat as the pattern fills
A dense grid can draw the fabric together if the thread is pulled tight. Smooth the cloth often and change the thread or needle if the spaces begin to close.
Do not judge the pattern after only one direction has been stitched. The final effect appears when the crossing rows are added, so give the structure time to develop.