Here are some ideas I loved but never used on how to take things out or make things longer. Maybe you guys will use them!
Extend a dress/skirt or top with a block of fun colored or matching fabric at the bottom.
Take out the sides of a dress but cutting out the some of the waist and hemming or cutting it out and adding a little stretchy fabric
Cut out the back of tight tops and add something decorative like buttons or bows.
images from jcrew, asos