Step 1: Materials
You will need a tank top with wide straps like shown. You will also need about a fat quarter of fabric. Cotton, preferably. Last you will need fusible interfacing and thread in the color of your choice.
Step 2:
First start by ironing on the fusible interfacing to the back of the fat quarter of your fabric.
Step 3:
Then fold the fabric in half with the interfacing facing out
Step 4:
Print out this pattern if you don't want to freehand it and trace or pin this pattern on your fabric, interfacing side. Line the folds up.
Step 5:
After you've cut it out, draw your own design on the rest of the cutout.
Step 6:
To cut out you can use an exacto knife but the faster method is the old-school snowflake style. You fold each of your designs in half and cut them out.
Step 7:
It should look something like this when you are done.
Step 8:
Now for the long and kind of tedious part: Sew around each of the cutouts. Also sew around the entire thing with a zigzag stitch to prevent massive fraying. It will still fray a little though, expect that.
Step 9:
To attach it to the tank, cut off the part of the strap you want to replace.
Step 10:
The fold over any new raw edges, pin, and hem.
Step 11:
Place your cutout in the spot you want it, overlapping the strap a bit for a secure attachment. Pin in place and sew.
Step 12:
It should look like this now.
Step 13:
And here's the finished product!