Use a small piece of fabric to make a pocket for the battery. Make it big enough that it's easy to get the battery out but not so big that the battery falls out on its own all the time.

Use a sewing machine or a needle and thread to sew the battery pocket to the inside of the skirt's lining, near one of the seams. Sew down three sides, leaving the pocket flap open at the top.

We want the battery and controller and switch on the inside of the tutu lining so it can't be seen, and the lights will go on the outside. Make a hole for the light connector to pass through the skirt near the battery pocket. 

I used the buttonhole foot on my machine to make a buttonhole to keep the skirt from ripping around the hole. You can also use a dab of fray check or fabric glue, if buttonhole-stitching is scary. (But .. here's your chance to learn!)

Put your Mini Sparkle Motion inside its case. Plug it in to the switch using your short USB cable or USB C/A adapter. Plug the switch in, and plug the other end into the battery. Plug the lights in to the Mini Sparkle Motion, going through the buttonhole with the connector.

Use a needle and thread or a bar tack setting on your machine to secure the switch and Mini Sparkle Motion enclosure down to the skirt lining.

If you're worried about wires pulling out -- like if this is for a kid -- you can sew another piece of fabric to the lining to cover everything up. Just make sure you can get the battery out for charging.

Flip the skirt around to right-side-out. All the electronics should now be hidden, and just the star strand will be showing.

I found it helpful to have my sewing mannequin, Betty, wear the skirt while I figured out the placement of the stars. 

Use sewing pins to pin the strands to the outside of the tutu lining. I used an up-and-down pattern, with three lights going up and three going back down again in a staggered zigzag around the skirt. Get them even by placing the connector between the strands at the other side seam, so you have one full strand across the front and one across the back.

Also note that the stars themselves are directional. The whole star glows but one side glows a little brighter since it's got the face of the LED on that side. I tried to place all the brighter sides facing outwards.

Now it's time to sew the stars in place. First: turn the strand off using the switch and/or unplug the battery. It's fine if you hit the wires with your machine accidentally -- it will still work with a few piercings through the wire, but you don't want your needle to accidentally cause a short circuit by hitting two wires at once. Sew while it's turned off.

I set my sewing machine to a 6mm wide bar tack, which is just wide enough to sew back and forth across the three wire strand without hitting the wires. Place a bar tack everywhere you have a pin, and anywhere else that's needed to keep the wires tight against the skirt.

This is also easy to do by hand if you don't have a machine, though it's definitely a bit more time consuming.

Make sure all your pins are out, flip the switch, and watch your lights glow!