To gather fabric start with a piece of fabric at least twice the length of your finished project. Gathers reduce the length of fabric.
Basic ways to Gather
By hand- sew a running stitch on the section you wish to gather, pull the thread to create the desired fullness. Tie off thread ends to hold gathers. Hand gathering works best on small projects.
Machine Gathers- use an all purpose presser foot. Set stitch length to longest stitch. Sew a straight row of stitching on the section to be gathered. Leave thread tails long. Do not back stitch. Pull bobbin thread only to create folds.
Alternatively you can use a zigzag stitch and cord. Place the cord along the section to be gathered and centred under the presser foot. Stay stitch the cord at one end then zigzag stitch down the cord length, encasing it in the stitches but not catching the cord. Pull cord to form gathers.
Finally other ways to gather fabric are by using elastic and gathering tape. Gathering tape is used in curtain making.