The best practice is buried in the article Clay linked, "Drag the appropriate action below the Failure path to direct the route you want the interaction to take. For example, a play audio action to indicate that the action wasn't successful, a transfer action to send the caller to an agent or representative for assistance."
That said, every organization (possibly every flow) is going to be a bit different, so you will need to assess the flow and decide what you want to happen for a particular failure. You might loop back around and try the action again, but limit it to two tries (using the loop counter), or you might just transfer to a live person, or perhaps send the caller to voicemail...it all depends on what is best for the situation.
Obviously, you want to cause the least frustration possible to the caller.