Step 1: Precisely cut a piece of fabric down to size - 27 inches heigh by 20 inches wide. Then fold the fabric over like a hot dog (wrong side up). You'll also want three long strips of fabric at this time.
Since I used a shower curtain that already had finished edges, I cut those edges off and used those for the strips because they were already finished and ready to go.
You'll need 2 strips that are 36 inches each (you could go shorter than this, I just like having a long strap). And then you'll need one strip for the neck that is 18 inches long. Each strip is a half inch wide, but you can do any width you like here.
Step 2: Then with the top of the fold to your left, measure over from the fold 4 inches and make a small mark (this will give you a total of 8 inches when unfolded for the top of the apron).
Step 3: Then measure from the opposite side (see photo) 18 inches high from the bottom and make a small mark. Then freehand a curved line from the mark you made in step 2 to the mark you made in step 3.
Again, see photo for reference. This curved line is the area on the apron under the arm.
Step 4: Cut on that line that was made in step 3, through both layers of fabric.
Step 5: Hem with a sewing machine, to create a finished edge all the way around the apron. Being sure to cut little notches on the curved parts (arm area) of the apron to help it lay / fold better for hemming.
Step 6: Next, it's time to add the straps. For the back ties, find the very end of the arm area, where the bottom of the curved line meets that vertical fabric line.
Then attach one of the long 36 inch straps to the back of the fabric. For added strength, make a square box with your sewing machine, over the strap. and then an X through it.
Repeat this step with the other 36 inch strap on the other side of the apron.
Step 7: Then, at the top of the neckline, add the shorter strap the same way you added the back ties in step 6. Snip any stray string to clean everything up and you're ready to craft (or cook).