What are you aiming for?
Renato Canova trains lots of the Kenyan marathon big boys. He says that the best way to approach a race is to build it up from the ground.
You shouldn’t be going out at a pace and hoping to hang on – the most important runs during the week are those which simulate your race, and the point of all the other training you do is to get you fit enough to run the simulations.
If you want to run a marathon at 7:10min/ mile, run weekly or fortnightly long runs including big chunks at that pace. All the other runs should be faster for shorter periods or recovering slower.
I’m running Leeds Half next weekend. On Sat I did 3miles@7:30m/m, 4miles@6:10m/m (target race pace), 1mile@7:30, 2miles@5:50, 2mile@7:30. I’m not as fit as I wanted to be after 3 weeks of being ill so it stung a bit at the end, but it was fun.
More here: http://tinyurl.com/4x6obmj