First I cut my tank top a little below the bust, leaving a little extra fabric to allow for the seam:
Next, I made a nice seam on my skirt fabric, made a gathering stitch, then gathered it.
Once I had everything sewed on, I tried on the dress to see where I wanted to cut the skirt off. I found a good spot, cut off the extra fabric, and gave it a nice seam. To finish it off, I used the extra fabric from the tank to make some flowers for the top. I used velcro to attach them to the tank, because I wasn't sure how they would wash up. I just take the flowers off before I wash the dress.