First press the dart as it’s been sewn, this sets the stitches into the fabric.
To prevent accidental pleats on the right side of the fabric always press from the right side using the toe of the iron to gently push and ease the fabric flat and away from the seam.
You can also use a thin piece of card under the dart to prevent the line of the dart being pressed through to the right side of the garment.
You may want to use a Tailors ham to give shape to the dart and a pressing cloth to prevent shining the fabric. Try and find the curve on the Ham that best matches the shape of the dart.
TOP TIP – using darts as a design feature can be an interesting way to add detail to a simple garment. Sew the darts from the right side of the fabric and top-stitch the excess fabric down to create triangle and diamond shapes.