Work with one square at a time.
Copy everything you see. Forget the big picture. Just copy all the shapes that you see (even the blurred ones).
First - mark the points where the shapes cross the grid lines. Think: "...this line crosses the grid about 1/3 of the square, or it crosses it right in the middle..."
Next - connect these marks. Make sure the shapes match.
Do not shade. Use only light fine pencil lines.