Sometimes it helps if you sight along the upright parts of the letters, to bring out the vertical lines.
Pretend you are a small plane coming in low, and you align yourself to land on those runways.
This will darken the main vertical strokes and make the cross strokes, including most of the cross lines, that much thinner so they tend to disappear. To read the cross lines, rotate by 90 degrees.

("vertical" here is relative. My handwriting can come close to a 45 degree slant.)

(Vertical astigmatism might help, too.)