When your hands are on the bed of the sewing machine, they should be about an inch below your elbows. As others have said, table height depends on your body measurements (torso and arms), your chair height (seat to floor), and your machine height (table to bed).
My table height is 33", the machine bed is 3½" above that, and my 'chair' seat is 24" off the floor. I am just 5'3" tall and prefer to sew in a semi-standing position using a stool instead of a chair. It's much easier to move around to cut, press, stitch, etc, and I can sew all day and all night without fatigue, without stressing my knees, and without blocking the circulation in my legs. It also means my sewing and cutting are done on the same surface (actually a hollow core door set on bookcases). I think table height should be a highly personal thing.