How to sew a cover stich ham, crossing another stich?

if the sewing machine is brand new, then take it back and get another one

http://www.singerco.com/uploads/download/3e3e5558857ed68836712ac8545abb48178772a5.pdf is the manual for your machine; look at p. 27. You want stitch 00, and then increase the stitch length with the up/down buttons on the control panel.

p. 24 of the pdf covers adjusting the top tension of the machine; you'll have an easier time of gathering if you reduce the top tension about 1-2 number setting.

here's a link for a manual

http://www.sewingmanuals.net/juki-model-lu562-amp-lu563-sewing-instruction-562563.html

SKIPPED STITCHES
1.the needle is not inserted correctly
2.the needle is damaged
3.the wrong size needle is being used
4.the foot is not attached correctly
if these suggestions don't help the the machine could be out of
time & the machine would need to be taken to a sewing machine
shop to be checked

Get into the practice of gently grasping and pulling the threads as you start your seam.

Do you have thread in your bobbin?
Is your needle fully inserted in the needle bar?
Is it the right needle for the machine?
Is your needle damaged, bent or dull?

CHANGE UR STICH SIZE AND TIGHT UR TENSION DISK

You can purchase that slide plate here:
Singer 758 Sewing Machine Slide Plate

Are you sure you have turned the foot button underneath the machine back to normal stiching and also then again for embroidary and have you placed the protective cover back for normal stiching once you removed the embroidary arm.

cover both sides with tissue paper, the firm kind,, then sew, remove paper, smaller stiches makes this easier