How to Make Straps for a Strapless Dress
If you're worried that your strapless dress might not stay up, make straps for it to feel more comfortable and confident. Decide what kind of straps you want, like a straight backstrap, a halter strap, or a cross back strap. Once you pick a style, you'll want to measure how much fabric you'll need to make your straps so you can buy the correct amount. Additionally, consider how thick you want your straps to be. After all of your measuring is done, you can pick a fabric that is the same color and texture as your dress. Then, all you'll need are a needle, some thread, and a bobby pin to make the straps.
Decide what kind of straps you want. Different straps will require different amounts of fabric, so before buying your fabric you will want to figure out what kind of straps you want to sew on.  The most common strap type is a straight back strap, where the straps are attached to the front and go straight over your shoulders, where they attach to the back of your dress. Another strap type is a cross back strap, where the straps start in the front on one side and then cross in the back and are attached to the other side of the dress in the back. The third basic type of strap is the halter strap, which attach at the front of your dress, go up your shoulders and tie behind your neck. Put on your dress. Once you decide what straps you want, you will need to put on your dress to get accurate measurements for your straps. You also need a flexible measuring tape to take the measurements for your straps. The measuring tape will mimic the straps of your dress so you can see how much fabric you will need. Pin one end of the measuring tape at the neckline of your dress. Wearing your dress, pin one end of the measuring tape where you would want your strap to start in the front of your dress. Both straps will be the same length, so it doesn't matter which side you are measuring from.  Make sure you are using the beginning of the measuring tape, the end of the tape that starts at zero. This will make measuring a lot easier. Swing the measuring tape over your shoulder. With the end of the measuring tape pinned in the front, put the other end of the tape over your shoulder. Reach back with your arm and pin or hold the measuring tape to where you would want the strap to attach to the back.  If you chose a straight backstrap, the measuring tape should be swung over the same shoulder. If you chose a cross back strap, the measuring tape should go over your shoulder and go diagonally across your back. If you chose a halter neck, the measuring tape should go up your front to the back of your neck. Note the measurement. Go to a mirror, still with the measuring tape pinned in the back or held in place with your hand. With your back to the mirror, look over your shoulder. You should be able to see where the measuring tape in the back is being held in place. Take note of the number in inches where the strap should end. Add to this number. You will want to make the length of fabric you purchase a little more than the actual measurement of the measuring tape. This gives you some leeway when you are making the straps.  For straight back and crossback straps, add four inches to the number. For instance, if your strap was 16 inches (40.6 cm), add four inches onto this so the final measurement is 20 inches. For halter straps, add about 12 inches (30 cm) on to this number. You will need enough fabric to be able to make a tie in the back, so you will need more excess fabric. Find a fabric for your straps that is the same color as your dress. After you have figured out the measurements for the straps, you will need to decide what fabric to use for your straps. You will want the straps of your dress to look like they match your dress. The easiest way to do this is to find a fabric the same colour as your dress.  Most fabric at stores like Jo-Ann Fabrics have fabrics organised by colour. You may want to bring your dress along with you if you are matching the colour of the strap to the dress. Find a fabric that matches one colour in your dress for patterned dresses. Finding the right strap colour for a patterned dress is less straightforward. Pick one of the more dominant colours in the dress and find fabric that matches that colour.  For instance, if your dress is beige with yellow flowers and green leaves, try to find fabric that is either beige or yellow, depending on what you prefer. Even though the straps aren't patterned, matching the fabric to the main colour in the dress will make the straps look like they belong on the dress. Find a fabric that complements, not matches, your dress. If you don't want your straps to match your dress exactly, you could also find a fabric that looks good with it, even if it's not the same colour. For example, if your dress is a pastel yellow, you could find fabric in a pastel green that would look good with your dress colour.  More extreme contrasts in color and texture may be more suitable for casual rather than formal dresses. Make sure the material of the fabric suits the material of the dress. If the materials look mismatched, the straps will look out of place. The easiest way to do this is to match the fabric of the straps to the fabric of the dress. For instance, if you are wearing a silk dress, find a silk fabric for the straps. You can also pick fabric for the straps that adds a decorative element to the dress. For instance, you can use a lacy or differently-textured fabric to liven up a basic dress. Buy enough fabric. Use the measurement in inches you calculated to buy enough fabric for the straps. Many fabric stores measure in yards. You will very likely only need a half a yard, though you may need more if you are making halter straps. Decide how thick you want your straps. You may want thin spaghetti straps, or you may want straps that are a little thicker. Decide in inches how thin you want your straps. Keep in mind that a slightly thicker strap could give you more comfort and security if you are worried about your dress slipping down.  If it's a formal or elegant dress, you may want to sew thinner spaghetti straps. If it's a casual dress, you could go either way. Multiply this number by two and add ¼ inch. This will be the measurement for the width of your fabric when you cut it. You need to multiply the number because you will be folding the fabric in half width-wise and sewing it to create your strap.  For instance, if you want your straps to be half an inch thick, multiply this number by two and add ¼ of an inch so that your width will be 1¼ inches. Cut the fabric. According to your measurements for the width and length of your fabric, cut the fabric. You may want to cut along a ruler to make sure that you are cutting straight.  For instance, say you calculated that you needed 20 inches (50.8 cm) of length for your strap and 1¼ inches of thickness. If you got a yard of fabric, cut a 20x1¼ inches rectangle. This will be the material you will use to make your strap. Make the second strap. Since you are making two straps for your dress, cut another rectangle the same measurements as the first rectangle. You can lay the first rectangle you made over the fabric and cut around it if that makes it easier. Fold the fabric in half. You may need to pin the fabric for it to stay folded. Make sure to pin near the crease of the fabric, because you do not want to put the pins in places that you will be sewing. Your fabric should be folded so that the wrong sides face outward and right sides, or sides you want to show, are facing each other.  You want the wrong sides facing out because you will soon be turning the strap right side out. Sew a ¼ inch allowance. Use a sewing machine or hand stitch to Sew down the length of the fabric ¼ inch from the edges of the fabric using a running stitch. Then trim the edges of the fabric to make the allowance slightly smaller. Make sure to use a thread that matches the colour of the strap. Do this for both straps. Cut a small slit on one end of each strap. Both of your straps should now look like tubes, with a little excess fabric after the seams. Take a set of small scissors and cut a small slit into the tube, about ½ inch from the end of each strap. Insert a bobby pin into the strap. Take a bobby pin and insert it so that one prong of the pin is inside the tube and one prong is outside. Push the bobby pin down the slit, still with one prong inside the tube and one outside.  You can also use a safety pin, but be careful not to prick yourself when using one. Work the pin out through the other side of the tube. The easiest way to do this is to scrunch the fabric of the strap around the bobby pin.  Hold the bobby pin vertically with the base of the pin facing downwards and the prongs facing upwards. Pull the fabric down by scrunching it until you see prongs of the bobby pin emerge out of the other end. Turn the tube inside-out. Grab portion of fabric with the slit near the base of the pin. Pull up. This will turn the tube right side out, so that the excess fabric is hidden inside the tube. Iron the straps. Now that the straps are made, iron them to make them flat. If you are having trouble getting the straps to lay flat before you iron them, safety pin the straps. Leave them this way for an hour or so and then come back and iron. Turn the dress inside-out. You need to turn the dress inside-out because you will be sewing the straps to the inside of the dress. This way the stitches will be less visible when you are wearing the dress. Pin the straps in the front. Place the straps so that they start two inches below the neckline of the dress. Pin them close to the top of the neckline, a little further down from where you will be sewing. Hand-stitch the straps to the inside of the dress. If your dress has a lining, sew the straps only onto the lining of the dress. This way you won't be able to see the stitching when you are wearing the dress. If your dress does not have lining, make sure to use thread that matches the color of the straps to make the stitching less noticeable.  Hand-stitch vertically so that the two inches of strap fabric is stitched against the dress. Then stitch horizontally about ¼ inch from where the straps hit the neckline. If you are sewing halter straps, this is the final step. Halter straps tie at the neck, so you do not need to sew the straps in the back. Pin the straps to the back of the dress. If you are sewing straight back straps or crossover straps, you will need to also pin and sew the straps to the back of the dress. Keep two inches of the strap below the neckline. Pin the straps to the lining about ½ down from where you will be sewing. If you are making crossback straps, you will need to cross the straps diagonally so that the straps are pinned to the opposite sides of the dress as in the front. Sew the straps in place. Follow the same sewing procedures as you did when sewing the straps to the front of the dress. Make sure that you are only sewing the straps into the lining of the dress if your dress has lining. 
Decide what kind of straps you want. Put on your dress. Pin one end of the measuring tape at the neckline of your dress. Swing the measuring tape over your shoulder. Note the measurement. Add to this number. Find a fabric for your straps that is the same color as your dress. Find a fabric that matches one colour in your dress for patterned dresses. Find a fabric that complements, not matches, your dress. Make sure the material of the fabric suits the material of the dress. Buy enough fabric. Decide how thick you want your straps. Multiply this number by two and add ¼ inch. Cut the fabric. Make the second strap. Fold the fabric in half. Sew a ¼ inch allowance. Cut a small slit on one end of each strap. Insert a bobby pin into the strap. Work the pin out through the other side of the tube. Turn the tube inside-out. Iron the straps. Turn the dress inside-out. Pin the straps in the front. Hand-stitch the straps to the inside of the dress. Pin the straps to the back of the dress. Sew the straps in place. 