It usually takes until my O shoes start falling apart until I stop getting blisters.
So compeed on each heal before the race usually works, although I have finished a race running in my socks cos my heels were bleeding but that was a long time ago.
However once you've got the blisters the only thing i've learnt is to not leave them covered up, even if they do sting, because then they take ages to heal.
On the subject of achilles problems, its what put me of damned V-J's.
i just dont see the point of that ridiculous heel!

apart from to give you nice blisters and kill you achillies