One day of speedwork, but no more than 20min,one Tempo run, no more than an hour, the rest all aerobic,the long run no more than 1/3 of your weeks total and do not increase your totals distance or time by more than 10% and every 4th week ease back.
eg. 4:30:00
4 x 5min with 3min recovery + warm up cool down total about 60:00
60:00 tempo
90:00 long run
60:00 aerobic
following week increase to 4:57:00 and so on.Thats my little system,but just read about Ed Whitlock who at 74 ran a sub 3hr marathon and did nothing but run for 3hr each day no weights stretching, core work just ran steady, so find what works for you and do it.