A friend this morning shared with me her rule of thumb for a successful marathon taper. It's very simple: 75% of your weekly mileage 3 weeks out, 50% 2 weeks out and 25% the week of. Another rule of thumb is to never run (in one day) more miles than the number of days you have left before the race. So if your race is on a Sunday, your long run the weekend before would not be more than 7 or 8, depending on the day you run. I like simple and these rules of thumb work for me.
What about you? Do you have a rule of thumb that you live by when it comes to a taper before your race?