Measure the back of your top and the space, where you are going to place the lace. Then cut a suitable piece of lace and sew it to the top.
If you want you can use a fabric glue, especially if you are not sure in your sewing abilities.
Basically that`s all – very quick and easy, but it does look awesome. What`s more you can experiment with lace shapes. In this case we use a rectangular piece of lace, but you can freely change the shape to a triangle, circle or a heart for example. Be the designer of your own style!