how to get the tension right on my machine?

my singer sewing machine 457 gives long stitches at the underneath of the material . what do I do to get it right again
Margaret Ping, April 2018


done
I don't have a manual.. Please show me how to set the numbers on a straight stitch, both tension and length

A.W, April 2020
my Primera NM800 the thread is not tight(loose) beneath the fabric I have tried all the numbers on the pressure tension but not working.
Can I also get the correct stitch length numbers for a normal stitch on a normal light fabric

A.W, April 2020
Double check you've threaded it correctly. Check the pull up and check the top tension control

sgfdsgds, April 2018
link Click here to see other fixes for Singer.