The ruffles are the easist part, you have to undo the inside leg seam to get them flat. You cut off as much of the legs as you are adding with ruffles. There's pics in the gallery here that my Mother did. I think the embellished ones are done by more advanced seamstresses; however you could practice with regular blue jeans and ruffles. Most of the boutique designers remove the bib pocket to do away with the thickness.
Good Luck to you.
Susan in Bama

There are two skills here. #1 is applique. You need the right techinque to make your stitches even and smooth, ad to that the right product of adhesive and stabilizer.

#2 you need to be able to make gathered ruffles either by hand or w/ a ruffler foot than attach them.

So there is your starting point, figure out how to applique... then move on.

HTH!
Tanya