Making new shoe string straps can be challenging, so there is a quick and easy way.  Buy yourself some Rats-tail Binding.  It is basically a very thin shoestring strap all ready made for you.  Then all you need to do is attach it onto the garment.  I have only seen it in a color black, but I am sure you can get it in other colors.  It costs around A$4.00 a meter.

If you can't get any ratstail, find some fabric that suits the dress and cut your straps on the bias.  Fold the fabric in half and sew 1/8th of an inch from the fold.  Cut 1/8th of an inch from the seam and use a turner to pull the strap in on itself.  You can buy a unit that allows you to push the strap through, but I find using a turner works well.

Happy sewing

Judith aka genie