Embellishments can turn a simple garment and transform it into something new and spectacular.  A good case in point - Mariah Carey's strapless gown with side lace insert.  Altering a pattern such as Vogue 2481 (which has a similar strapless, gathered side seam design) to include an insert is a relatively simple change.  Purchase a wide cutaway lace, removing the same width from the pattern piece(s). Be sure to leave seam allowances in your pattern, otherwise you will alter the fit of your dress.  Create a finished edge to the in the areas you plan to insert the lace and stitch the trim over this edge on the right side of the garment.  But don't stop at dresses, this is a great way to spice up your favorite top or even pants pattern!