I made the infinity dress mostly following the instructions on knucklesalad. However, I thought it would be really useful to have a step-by-step, and the ones on Instructables aren't quite the same. The kind I make has a very useful component, the "waistband", which lets you wear a bra with your dress!

I highly recommend you make one or several, regardless of your previous sewing experience. As long as you have access to a sewing machine, this is a dress you can make in under an hour. And it's very comfortable and versatile!

Step 1: Measurements

You will need to measure:
(1) height
(2) waist
(3) center of chest to armpit (just above boobs)
(4) bottom of sternum to top of boobs

(See the pictures, in order by number.)

Step 2: Fabric

When you are fabric shopping, you need to look for a stretchy, jersey knit fabric. These dresses look great in one or two colors.

Straps/waistband: 1.5 x your height.

Tip: Get fabric that looks the same on both sides. It will look better when you do your wraps!
Tip: Find a friend, or make two dresses! The straps are long and skinny, so there will be enough width of fabric left over to make a second set of straps. If you do this, add 2x measurement 4 from the previous step to the length so that you have enough for both waist bands.
Tip: You can get away with less length of straps if you want. I did one that was a couple of feet short and it still worked, though it wasn't as versatile.

Skirt: you will need a square of fabric, so get the same amount of length as the fabric has width (1 & 2/3 yards for 60" fabric or 1 & 1/4 yards for 45" fabric).

Tip: Your skirt length will be a little less than 1/2 the width of the fabric.
Tip: Make sure your fabric isn't too thin! Some fabrics are a little see-through when you wear them as skirts.

I chose the fabric above: the black & white pattern for the skirt and the red for the straps.

Step 3: Cutting

You may find knucklesalad's guide helpful as well: http://knucklesalad.com/wp-content/uploads/2010/06/InfinityDressDiagram.png

Cut out the skirt.

Fold the square of skirt fabric into quarters.
From the corner which does not touch any edges of the fabric, measure out half of the width of the fabric (so if it's 60" fabric, measure 30"). Use this measurement as the radius for an arc, where the folded corner is the center of the circle. Cut on the arc.
Now cut the waist. Calculate the radius you need from (your waist - 3") / (2 * pi)- for a 26" waist, about three inches.
Tip: Cut the waist a little small, then try it on. You can always cut a bigger hole!

Cut out the straps.

Fold the straps fabric in half lengthwise (selvage to selvage).
Use your center of chest to armpit measurement (measurement 3). Measure up from the selvage for the length of your fabric.
Tip: If you're making two sets of straps out of this fabric, leave some length on the end to cut your waistband.
Cut the long straight line to get your two long, rectangular straps.

Cut out the waistband.

Keep your fabric folded lengthwise like it was for the straps.
From the fold of the fabric, measure down 1/2 of (your waist - 3").
From the edge of the fabric, measure out 2x the bottom of your ribcage to just above your boobs.
Tip: if you're feeling lazy or don't understand that measurement, just cut in the realm of 14-20".

Step 4: Sewing

Sew the waistband into a loop.

Right sides together, sew the seam that is twice the length of the bottom of your rib cage to the top of your boobs.
You can use a straight stitch.
Fold the loop in half so that the wrong sides are together.

Sew the straps to the skirt.

Right sides together, sew the end of a strap to the circle you made for your waist.
Tip: It may be easier to do this if you don't pin.
Tip: Use a stretch fabric or zigzag stitch so that your seams can stretch.
Sew on the other strap in the same manner. Make the straps overlap by half of the width of one strap.

Sew the waistband onto the skirt.

Place the raw edges of the waistband on the outside of the circle, sandwiching the straps.
Tip: Be careful here! Look at a picture of the finished project and poke around at your piece to make sure that everything is in the right order.
Tip: Pin this one. You might need to stretch something as you sew to make them fit together properly.
Sew with a stretch or zigzag stitch.

And that's it! Now you have a dress!

Step 5: Wearing

I'm showing only one configuration of the dress here, but there are many options- and tutorials- which you can find easily on the internet. With this version of the dress, you can wear the waistband up to cover your chest or down for a more daring configuration.

Dance, twirl, walk and swish- enjoy your dress in all its arrangements!