I picked up this bed sheet at a second hand store for about $2.50. I was looking for something to make simple curtains with, but the print looked like it would make an interesting dress, so I couldn't resist.
This is a very simple dress, made of only two pieces of fabric with a simple elastic waist.
DESIGNING A PATTERN FOR YOUR BODY:
I folded the sheet in half lengthwise, with the right sides together, and laid it down on a flat surface. I found a similar dress (made of a fabric with no stretch, and with a simple elastic waistband) within my wardrobe, turned it inside out, and laid it flat on top of the sheet, with the hem of the dress about 2 inches from the bottom edge of the sheet. I traced the rough shape of the dress onto the sheet, adding an extra inch on all sides for seam allowances, while fully stretching the elastic waistband to see the actual width of the fabric. I freehand drew the sleeves, allowing for a generous arm hole opening (they're very simple - again, look at the armhole openings of clothing in your wardrobe to see the shape that suits your body best). In reaching the bottom of the dress, approach the end at a 90 degree angle so the bottom hem will appear rounded (see photo). If you approach at an angle, the seam will form a point.
Pin fabric together, cut out the two pieces. Unpin.
Hem sleeve openings, folding raw edge underneath and sewing with 1/2" seam allowance. This leaves raw edges inside, but for me, it was fine. If you have a Serger, you can machine finish the edge before you fold and hem. If you haven't a Serger, you can finish the edge by hand with a needle and thread after you fold and hem. It's a little bit time consuming, but it works, and will prevent the edge from fraying and make the item last longer.
Freehand draw a neckline on one of your two dress pieces to make the front. For a guideline, take a look at some of the necklines of items of clothing/dresses you own. Err on the side of caution: don't design the neck opening too large. You can widen an opening, but you can't ever make it any smaller once you've cut it. Try pinning the two sides together at the shoulders and pulling it over your head to find a comfortable and flattering size. Allow 1" for seam.
For a nice neckline in the back, lay the front of the dress over the back WITH WRONG SIDES TOGETHER, RIGHT SIDES OUT. Look through the front layer to the back and draw a slight dip on the neckline of the back layer. Make the dip as subtle or as dramatic as you want (I went pretty subtle, myself).
Disclaimer: this isn't the fanciest neckline in the world, but you can dress it up with imagination.
Hem neckline openings - begin by folding and pinning the edges underneath, keeping the front and back pieces of the dress separate. Clip the edge of the fabric with tiny snips of scissors as necessary, to help edges fold underneath more smoothly. Sew with 1/2" seam allowance. Hand finish the raw edge.
Now, take a moment to see the shape the dress is beginning to take. With right sides together, pin front and back pieces together at the shoulders, and all along the top edge of the dress, leaving the neckline open. Turn the dress right-side out and pull it on over your head. How does the neckline look?
Pinch the edges of the dress together around your body to ensure you've allowed enough space for yourself (if it's too tight, it may be game over).
Pinch the edges together under the arm holes. If armholes are too tight, consider widening them (you would have to re-do armhole seams, so avoid this unless necessary).
Once you're confident that the dress is coming along without any major problems, you can begin sewing the front to the back. Sew along the top of the sleeves and the shoulders; sew down along the sides of the dress. Turn right side out and try it on!
Now, for the waistband. For this particular dress, I decided to be a little excessively crafty by using the elastic waistband from a pair of undies that I never wore. It's a good way to get a suitable width for the waist of the dress (you can sew the elastic ring a little smaller to make up the difference between the size of your hips and your waist). For a more polished look, use an actual elastic. Choose one about 1/3" wide. Measure your waist, and cut out the equivalent length in elastic, allowing about 3/4" for sewing the ends together.
Turn the dress inside out. Slip it on. Pull the elastic ring over your head and body, to the spot where you'd like the waist of the dress to sit. Mark the spot by making a small dot on the raw edges at the sides of the dress (do your best to make these marks symmetrical or your waistline will be crooked). Take off the elastic and the dress.
Now, this is kind of hilarious and silly, but bear with me - it works, and I don't know any other way. Keeping the dress inside out, stuff it with pillows until the dress is firmly padded all through the area of the waistband. Then, slip the elastic ring onto the dress shape, placing it where you marked the waistline. If the elastic pinches the pillows and makes the fabric gather, you'll have to stuff the dress with more padding. Once the fabric is stretched taught around the padding, pin the elastic in place.
Using a needle and a long length of thread, baste the elastic in place all around the dress, removing pins as you go. Basting is a simple, straight stitch that holds things together before finishing with a machine. You can make it quickly as it doesn't need to be beautiful, and can be removed later.
With the elastic now basted in place and all pins removed, remove all the
padding inside the dress. Turn the dress inside out, and machine sew along the line you've basted, using a zig-zag stitch. You'll have to pull on the elastic to fully stretch it while you sew, keeping the fabric taut. This is a difficult line to sew, as it's at the middle of the dress. A lot of fabric will be bunched up by your right hand. Be careful to keep your workspace organized and your dress moving around the machine.
Following this, remove the line of stitches you basted. It should just take a few simple snips and you can pull out long lengths of the thread. Try it on, see how it fits! If you prefer a shorter dress, hem the bottom. For fancier sleeves and neckline, try fabric edging or lace.