The first step is to finish the seams that will be joined. Always apply a seam finish before you join a seamed piece of fabric to another piece of fabric. Once the fabrics are joined, you can not reach the entire seam allowance to apply a seam finish.
Always thoroughly press the seam before starting to join two seams.
A facing should be prepared with interfacing and an edge finish before it is joined to the body of the garment.