|I use elastic thread all the time in making clothes for my daughter. You can easily make a fitted halter dress for the summer with this technique.
You can find elastic thread at any fabric store with a good notions supply. It can be found with the rest of the elastic, not the thread.
1. Hand wind the bobbin with the elastic thread and don't pull it.
2. Use regular thread for your top thread.
3. Set your stitch lenght to the longest stitch and I usually set the tension around 3-4.
4. Cut your fabric with at least a 2:1 ratio for the size you need. For my daughter I cut a piece 10"x22" for the back of her dress.
5. Hem the top of the piece first. It is difficult to do when it is all bunched up.
6. Start sewing in long straight lines. You can trace your guidelines if you want or just go slowly. I use the sewing lines as a guide for distance. I go down three stitches in between each line.
7. When you are done sewing your lines, tie the two threads together. It is hard to use and anchoring stitch with the elastic thread, so tying them together is necessary.
8. Now if it didn't shirr enough while you were sewing, you can use a steam iron to bring it out. It usually shirrs more when I put the outfit in the dryer, too.