The ulitimate goal for sewing stretch fabrics is that you don't
stretch the materal as you sew. It's tempting, but the only time your fabric ever stretches is when you're trying it on you to see if it fits properly.
Now, if for some reason that you don't have the stretch-stitch option on your sewing machine, the classic ziz-zag stitch can work just as well.
I hope this helps