I think this project – giving a pair of shoes an update with new fabric-covered heels – was inspired by Gok Wan on TV a while ago...
Make a template for the heel shape (which is very different to how you might imagine it, I promise) by sticking on layers of sticky tape.
When you've got a thick layer, draw a line around the edges of the heels.
Now peel off the sticky tape, and cut around the line.
On your fabric, draw around the sticky-tape shape and cut out. Stick it on the heel with fabric glue.