In this illustration the floss is in an up position to start with. Notice that your needle goes through the pleat straight. Your thread falls naturally in the down position. Tug the thread gently parallel to the pleat to tighten, then move onto the next pleat. Continue this pattern across your row to the end of your pleated piece.
Consistency is the secret to beautiful smocking.
Making your stitches even and smooth, placing your needle along the same plane pleat after pleat. Once you get the pattern down and you get a rhythm going and the alpha wave length kicks in and the kids, dog and irritated husband disappear. Ah, this is the reason why we smock. Your stitches should be pulled tighter than shown here. Completed cable stitch.