ONCE YOU HAVE FINISHED stitching your seam, it’s best to press it open on the wrong side so it lies flat. Sometimes it’s better to press it to one side to reduce bulk but the pattern instructions will tell you this.
Usually the seam allowances are left as they are as they help to strengthen the seam, but sometimes they cause too much bulk so they are trimmed to half their original width.
If your fabric has a tendency to fray you should neaten the raw edges after you have worked the seam. There are several ways of doing this. To machine-finish them, set your sewing machine to the zigzag stitch then stitch close to the raw edge all the way along. The zigzag must be small enough to stop the fabric from fraying but large enough to enclose the bulk of the fabric. Practise a few lengths and widths before you begin. Alternatively, you can trim the raw fabric edges with a pair of pinking shears. If you have an overlocker then you can stitch, cut and finish the seams all in one process.