(fot the knot also see http://icancu4more.blogspot.co.uk/2013/01/diy-hand-stitched-wash-bag.html)
Start stitching. I loop the first stitch around to the back and up very close to the first hole which seems to give it more hold. Then sew in a straight line a straight stitch.
The stitches should have a nice rhythm. Too wide leaves a gap, too narrow might ruin the fabric. When you reached the end run your finger along the stitching from the beginning to the end to find the right tension between fabric and thread. Too tight and the fabric looses its stretch, too loose and the thread makes loops.
Finish as you started. Loop the last stitch around to the front and down next to the same hole, make a double knot in the same place (on the wrong side) by using your nail and a single knot further away, trim the thread. Ideally both knots the first one and the last one are on the same side.
STEP FOUR
Pin the seams to the side where your knots are (so they will hide under the seam). Thread your needle, it is nice to use a contrasting colour for this eye-catching cross stitch.
The start is the same as for the straight stitch by looping your thread around the edge. Come up next to the loop and make the first bottom part of the cross stitch, the needle should come up at the same distance from the edge as the stitch that came up next to the loop. The top part is exactly the same as the bottom part but moved to the right and you come up at the same distance from the edge as the last stitch that came up on the bottom. . . Keep your top and bottom parts of your cross stitch in a line so your stitch looks regular with a nice rhythm. In the last pic you can see the wrong side.