First take any dress pattern (only the base) that fits the girl for sewing and fold it so that one shoulder (including sleeves) is obtained is hidden. Now place it on two layers of fabric (right sides together). Outline and cut.
 

Now let's make the ruffles and a shoulder strap.

Cut 4-inch wide strip for ruffle, the length of which shall be equal to the two dimensions of cleavage. Please note: this dress is off the shoulder, to the neck means the neck + one shoulder. Please note that the width of my quilling is much less than 4 inches (and I deeply regretted it). If you want the dress to look exactly as I have, you can keep the width 2.5 cm, but I strongly feel that you should do with a wider ruffle.

For shoulder strap, cut a strip approximately 3 cm in width and 10 inches in length. You are probably not using all 10 cm, but I usually keep some amendment to adjust it then on the child.

Now on to the sewing:

Sew one shoulder seam and both side seams of the main part, set it aside:
 

Now pleat or frill ruffle so that the final length is close (slightly larger) neck circumference.
 

Shoulder strap just sew strips of 10 inches in length, right sides together. To turn inside out to make up.
 

Now sew the shoulder strap to the dress. Turn the dress inside out so the right side was on the outside. Select the place (front and back) where you want to sew the shoulder straps. I have it 7 inches a year and a half.
 

Now, add ruffles, and ruching at neckline.
 

Now turn the ruffles right side. The dress is ready for fitting. 

If you feel that the shoulder strap, big or small, you can set it up now, picking stitches from one end, where it has an extra tail and to increase or decrease length. Sew the tail as soon as you're finished.

Most of the dresses I've seen in gymboree or GAP had only one ruffle, so this master class is enough. 

And now I will show you how to finish the armhole.

Cut a strip approximately 15 cm with margins:
 

Sew it along the armhole (right sides together).
 

Now flip it over on the seam on the wrong side of the armhole. Topstitch.
 

Since knits don't fray I didn't care to hide the raw edges. You can do this if you are working with textile goods, not knitted.

Now, let us give the dress some pizzazz:

Cut two strips:

C1: 7 cm wide x 100 cm
C2: 5 cm wide x 100 cm

C1 to sew on the longest stitch installation along one side of the lane. After flashing pull the bobbin threads from one end to create the ruffle. To distribute the gathers evenly. Sew the Ruche under the ruffles that are already there along the neckline. Make sure the top ruffle completely covers the seams. Now Topstitch the top ruffle along neckline.
 

For the ripple at the hem, take the strip S2 and to perform the stitch in the center, again on the longest stitch installation. Again pull the bobbin thread to make the ruffle, but this time with the ruffle should be just before the hem. Evenly distribute the ruffles by hand. Now sew it to the hem. Since this is knit, I didn't bother finishing the hem, you may have to do it.
 

If you want, you can add a flower on the shoulder strap.

Enjoy your new dress.