At first I was terrified of working with knits. I’ve come a long way since then, and I enjoyed reading this refresher from Crafting for a Green World:
So, whether you’re remaking an old rock concert T-shirt or sewing a skirt from a thrifted jersey sheet, here are the three stitches you need to know to do the job well:
1.The zig-zag. A zig-zag stitch is perfect for knit fabric, because it stretches with the fabric, and thus is less likely to pucker or cause thread breakage. Choose the narrowest zig-zag stitch that will not pucker or stretch your fabric, since the wider/longer your stitch is, the weaker it will be. When sewing a seam, you can partially encase the raw edges by allowing one side of the zig-zag stitch to go slightlyover the end of the seam, mimicking an overcast stitch on a serger.
2.The mock overlock. Even older sewing machines often have something like this stitch, although it goes by a variety of names and faces. The stitch looks something like an X with a horizontal line at the top and/or bottom, or perhaps a V with those same horizontal lines. This stitch, if you have it, is even sturdier than a zig-zag, and can also be used to finish your seams, though it’s also wider and uses more thread. It’s best for seams that will get a lot of stress, and not for smaller, more delicate pieces.
3.Anything but a straight stitch. Really, the only stitch that is completely inappropriate for sewing knits is the straight stitch. A straight stitch has no margin to stretch with the fabric, and will simply break.
Read more here. Happy stitching!