Working with CurvesConcave curves: In general, it's often easier to turn under a concave curve (a curve that moves inward, like a bite out of a cookie) if you make perpendicular cuts towards the fold like.
Convex curves: Convex curves bend outwards, like a rounded hill. There's usually no need to make clips into a convex curve.
Working with PointsOutward points, like star tips: Sharp points can become bulky from multiple layers of fabric created when raw edges are turned under for sewing.
- Minimize bulk by (temporarily) ending your seam a couple of stitches before you reach the end of the pointed tip, and trimming away a portion of the remaining seam allowance along that side.
- Now cut off a portion of the seam allowance above the point itself (straight across) and fold what's left straight down, perpendicular to the point.
- Fold under the upper sections of the next side of the point and continue sewing. Use the tip of your needle (or a toothpick) to coax fabric into place if necessary.
Inside points, the reverse of a pointed tip: Clip straight in to inside points, almost to the seam allowance. Stop sewing a few stitches before you reach each inside point and turn under the seam allowance on both sides of it. Continue sewing, taking a few extra "security" stitches into the pointed area where the seam allowance was clipped.