Stitch. I am having a problem with one type of fabric, my sewing machine go crazy when i sew

Question

I am having a problem with one type of fabric, my sewing machine go crazy when i sew velvet I need the normal straight stitch , what happens is that the stitches are not even or equal and sometimes suddenly I find the thread out of the needle , how come!!
I am havinf a problem also how to know set the foot pressure for every fabric .... what can i do pleaseeeeee??