I suggest you shop ready to wear first, armed with a notebook, tape measure, and the determination to hunt down some ideas and guidelines to equip you at the sewing machine. Observe colors, lengths, sleeve styles, and neckline features you like as you browse and try on ready-made dresses. These four elements are usually the most important factors for a garment you'll ultimately feel good in.
Once you have made these discoveries and written a few basic notes to yourself, head for the fabric store with measurements and perhaps even a few sketches/photos of what you've seen in your shopping excursion.
At the pattern counter, look for a pattern that catches your eye at first glance. It doesn't have to be something complicated. Selecting a dress pattern with few seams is fine but you may also want to look for a style with princess seams as these afford a bit more fit insurance. For a loose fitting dress pattern pick a size that's close to your high bust measurement. High bust is a snug measurement just above your full bust. Unless you have a large cup size this size is usually more accurate for a garment that hangs from the neck. For additional fit insurance add 3/8-inch to the pattern tissue at the side seams, providing a generous 1-inch seam allowance. When sewing, baste the sides using the 1-inch seam allowance, fit the dress, and adjust as necessary. Remember you can always trim away excess. This is by no means the be all and end all of fitting guidelines but unless you have a lot of specific fitting issues this should be a good start.
As usual, I suggest making a trial garment from inexpensive fabric to work out the fitting issues. You just might end up with a winner in your trial garment but at the very least you can pin, stitch, and cut this test piece as needed to fine tune the garment. Don't feel obligated to finish it, it's okay to call it a test and be done with it. Now, transfer the changes to the pattern and proceed to shop for your final garment fabric.
The dress you see here was a result of my desire for a summertime dress that I could wear when I wanted something just a little bit special. I turned it into somewhat of a color block dress with a semi-sheer asymmetrical overlay and added machine embroidery. This pretty in Paisley dress was featured in a past issue of Designs in Machine Embroidery magazine.
To read more about It's Sew Easy episode 806 CLICK HERE to read my previous post. CLICK HERE to go watch the show. Enjoy!