There are so many seam finishes out there it can be difficult to decide on one. The decision is typically made based on the type of fabric and the exact look you're going for. If you're hoping to hide all your raw edges by enclosing them, and your fabric is sturdy and does not fray easily, or at all, you might consider the self-bound seam.
Start by ironing your seam in the expensive position. This will help keep you from accidentally clipping both sides of the seam allowance. When it's nice and flat, trim one side to about 1/8". No more than that, but not really less than that either. You'll need the room.
Once that's done, fold under the opposite seam allowance and press carefully. Fold it under again and press again. Then take the trimmed seam allowance and slip it inside the folded seam allowance. Take your time and make sure everything lays flat along the entire length of the seam.
When you're prepared, stitch the seam closed. Stay as close to the folded edge as possible while still catching all layers of the seam allowance. Once you're done, press flat and go.
