Gathering is pretty easy, but can be a pain if your machine doesn't have a gathering stitch or if you set your stitch length to small. Here I will give a step by step tutorial on how I gather for skirts, dresses, aprons, etc...You can click on the images to blow them up on your computer screen for a better view.
1. To gather I usually use a basting stitch set at 1. This gives me a pretty loose stitch and makes it easy for me to pull the thread that creates the gather. It spaces the gathers a nice distance apart and allows you to move the gathers closer together or further apart depending on your preference. If you go smaller than 1 you might find that the stitch lengths are too small and too close together causing your thread to break mid-way as you are gathering.
Start about 1/4" from the edge with a normal stitch and back stitch 2 or 3 times to secure it and then start the gathering stitch:
2. Sew the gathering stitch all the way around the edge and when you get back to your starting point keep going 3 0r 4 more inches. Don't back-stitch at the end. Lift your presser foot and pull your fabric out from underneath pulling on the thread as well. You a 3 or 4 inch thread to pull on to create your gather:
3. Take your ending thread on the top of the fabric and gently pull to create the gathers. Once you have gathered your piece you can attach it to your other piece.
4. When sewing a gathered piece to another I usually sew with the gathered side facing up so that I can make sure it is even and that none of the fabric in between the gathers moves below the stitch I am sewing:
(I also have an alternate way to gather if you are having trouble with your thread breaking a lot. It's also great for gathering heavier material or large pieces like bedskirts.I'll try to get that posted in the near future.)