Gather each long side of each trapezoid. You can do this easily by adjusting the thread tension and the stitch
length to the highest setting. Then measure to see how long it is, and if you need to gather it more to make it equal to the waiste-floor measurement, then gather it by pulling on the top thread, while guiding the fabric up the thread to create a bigger rufle.
Repeat the last step for the rest of the 7 pieces, then sew them all together, with, of course, the raw edges on the inside. Serge or zig-zag stitch each hem, so that it is reinforced as a gathered hem, not just the individual hems.
Once your skirt is in skirt shape, make a V in the front to allow the V shaped bodice to easily attach. The V should be about 2 inches in depth, starting from the sseam that will lay on the hip, to the other hip, as pictured below.
Sew a line around the top of the skirt using the same technique for a gathered seam. Then, pull threads again to match up with the waiste measurement you took.
Next, we're going to add the embelleshment to the bottom. You're going to need a very long strip. How long, is dependent on what size of dress you are making. In the picture it says it's equal to the width of the skirt at the portion it will be placed on, times 1.5, since it needs to drape a little. This is approximate, of course, so make sure you double measure. Measure around the portion of the dress that the embellishment will go on (around 8-16 inches off floor, depending on size of dress), then add a few inches as needed to get the total length of this strip. The idea is that this strips drapes 2-3 inches per section. The height will be around 5 inches.
Next, you will fold the strip in half, with wrong sides out, sew down the edges, and pull inside out to reveal the right sides. The height should then be about 2 - 2 1/2 inches, depending how big your hem was. Reinforce hems as necessary.
Next, you are going to gather the strip. Lay it against the dress, and make sure it drapes a little per section. Place a pin on the strip where each section of the skirt meet. Then gather where those pins are as illustrated.
Attach to skirt. Make sure gathers correlate with the seams on the skirt.
Cut a line down the middle of the bigger of your front pieces. This will be that seam that most Disney princesses have down the front of their dresses. Put right sides together, and sew a 1/2 inch hem. Reinforce hem.
Now we want to attach our front pieces. Put right sides together, with the hem from the top piece facing outward, as pictured below. Then sew together where the picture show a red line.
Then flip inside out so the right sides are facing out. Sew along the entire outise, including going over (as close to the edge as possible) the seams we just made that are now on the inside.
For the back, Cut a line down the center. Then hem up the sleeves as shown.
Do a zig-zag stitch, or serge the edge of each side that you just cut. The x2 means do it for each side.
Fold and iron down 1 1/2 inches from the edge, over to the backside, as pictured. Then hem the neckline over top. Do this for both sides.
Make a pencil marking (or mental note) of 1 inch from the edge on each side. This is where your buttons will be. Make sure you measure again and again where your buttons will be to make sure they are even. You'll want to be sure there are at least 1 1/2 to 2 inches between buttons, so we can add embellishment later. Since all sewing machines are different, I will assume you know how to use yours to make a button hole. Most sewing machines have a stitch option for this. Consult your owners manual to learn how to use it, if you don't already know.
Then, attach the back of the top to the front of the top. Reinforce hems as necessary. Measure the width to make sure it correlates with the waiste circumfrance and the chest circumfrance.
Now for the Top embellishment.
Cut a strip of fabric (the same fabric as the embellishment for the bottom) that will fit around the top of your little girl's arms right at the shoulder. It needs to be long enough to wrap around the back inside panels about 1/2 to 3/4 an inch. It also needs to be about 6-8 inches in height, depending on the size of dress you are making.
Next, fold that piece in half length wise, and sew along raw edges as shown. Sew along the red line.
Sew along the red lines and gather. The raw edges on the very end need to be serged or zig zagged, or even heat sealed, if the fabric is some sort of synthetic fabric.