E-Textile Mask
This Tutorial is Retired!
For an updated E-Textile Mask tutorial, try checking out the "Illuminated Mask" tutorial.
View the updated tutorial: Illuminated Mask
Gella 
Step 3: Ready, Set, Sew!
If you need help sewing with conductive thread this tutorial covers the basics.
Using a long piece of conductive thread (~2 ft) begin sewing the positive ends of the LED to your battery holder in a line. You can use one piece of thread and sew along to the first LED, sew 3-4 stitches through the hole to secure and instead of knotting and cutting, continue on to the next LED and repeat until you've reached the end of the row. Then tie off and cut.
Repeat for the negative sides with a separate piece of thread. Make sure each LED has 3-4 stitches around the hole to secure tightly before moving on.
Try a 'wiggle test' – if you can easily wiggle the LED back and forth after stitching it, the stitches are too loose and your connection isn’t secure.