Flat Fell Seam:

This is a strong, self neatening seam which is often used in soft furnishings. With right sides together, edges matching, pin, tack and stitch the fabric, taking a 0.5" (12mm) seam allowance. Trim down 1 seam allowance to 0.25" (6mm) ( See figure 1 below).

Fold the wider seam allowance in half to enclose the trimmed seam allowance (See figure 2 below).

Press the folded edge against the fabric (See figure 3 below).

Pin, tack and stitch down the seam, close to the fold (See figure 4 below).

Figure 4

Figure 5

Figure 6

French Seam:

A self neatening seam which is usually used for sheer fabrics. With wrong sides together, edges matching, tack and stitch the fabric, taking a 0.25" (6mm) seam allowance.

Press the seam flat and trim to half it's size (See figure 5 above).

Refold the fabric with right sides together.

Pin and stitch a second seam just big enough to enclose the raw edges (See figure 6 above).

Flat Seam:

Place the fabric pieces with right side together, matching raw edges.

Pin, tack, and stitch 0.5" (12mm) from the raw edges.

Press open.

Work a few stitches in reverse at each end to secure.

Gathering:

Gathering is used to add frills. A frill before it is gathered needs to be at least 1.5 times it's finished length but making it twice as long gives a much better effect.

When gathering on a sewing machine, use a heavy duty thread on the bobbin for extra strength and loosen the upper tension slightly.

Stitch across the fabric just inside the seam line.

Work a second row of stitches 0.25" (6mm) above the first (See figure 7 below). 

Gently pull the bobbin threads from one end feeding the fabric evenly down the gathers.

Wind the threads in a figure of eight round a pin at the side when the required length is achieved (See figure 8 below).

Instead of machine stitches a small running stitch can be used (See figure 9 below).