You will need...
Tip: use a scalpel with a fresh blade, as it's likely to be at its sharpest.
In the interests of safety, it helps to be dexterous with a scalpel and glue gun. However, this is basically an easy, straightforward, what-you-see-is-what-you-get project.
About an hour.
Get your fringe on
Decide on a design and cut out the shapes you want to use, making sure they're symmetrical and consistent on both shoes.
Cut the shapes into fringing with slits about 2mm apart (eyeball it!).
Glue the pieces on top of one another, then stick them underneath the t-straps.
It really is that simple!