If you are working with a pattern designed for woven fabrics, you'll need to open it up to determine the finished garment dimensions. Many patterns have these printed right on the tissue. If not, you can figure these out by measuring across the pattern pieces along the waist, bust, and hip lines. Don't forget to subtract for the seam allowances: If a garment has four seams, and each seam is 5/8 inch, then you need to subtract 8 * 5/8 inches. Compare these measurements to your own body, and cut the size that matches yours. This is generally 2 to 4 sizes smaller than your usual size, depending on how much ease (bagginess) was designed into the pattern to begin with.

It will save you some time and effort if you alter the pattern to suit your measurements before you cut out the garment. Most patterns have places marked with double parallel lines where you can lengthen or shorten the pieces as needed. The Kwik-Sew book shows step-by-step how to make these kinds of alterations.

If you're making a dress with a waistline and attached skirt, then you can just cut out and sew the bodice and deal with the skirt later. If you're making a panelled dress, then you need to plan out the lower part of the dress now. Say your dress is a 8-panel princess seamed dress, and you want the finished diameter to be 16 feet. You'll want the bottom edge of each panel to be 24 inches, then...but you should add another inch or two to account for the seam allowances, too. Find the center of the waistline of the bodice piece, and measure straight down from there as many inches as you need the dress length to be. You can determine that measurement by measuring your body from your waist to where you want the skirt to end. Add two inches for the hem and possible mistakes. Mark the fabric at this point, it's the center of the bottom edge of the panel. Now divide the desired panel width in half, and measure out from the bottom center mark in each direction. For my example, you'd measure out 13 inches in each direction (1/2 of 24 plus some extra to account for the seams). Mark each of these endpoints, they are the outer corners of the bottom edge of the panel. Now connect these outer corners up to the outer edge of the waistline on the bodice pieces. The last thing you need to do is smooth out the curve where the line you drew for the skirt connects to the waistline. I highly suggest using a dressmaker's curve or a French curve. These are pieces of plastic in the shapes of curves that you can use to connect the areas and smooth out the angles. You can buy these at well-stocked sewing stores.