One thing I am really intrigued about and would like to try is doubling up i.e. running twice in one day. One suggestion is to add easy morning runs of three to five miles on hard workout days. This is both a good way to add mileage and doing this way helps you learn to run fast on tired legs.
The problem is I really don’t want to overdo things and find myself injured but I confess I am totally intrigued by the concept and would definitely like to try this.