Running is the most aggressive sport. It is you against everyone else in the race (including yourself)and only one person prevails. You have to have a plan. How are you going to defeat those odds?
Lack of aggression is the biggest mistake runners make. Summer training is not just long easy running. This is the time when you experiment with aggression. You build an arsonal during the summer. I used to start my runs with the fastest mile I could do (4:07 was my best) and then run the entire 10 mile workout for time.
Summer is a great time to learn a sudden sprint that devistates the competition with its quick beginning and ruthless speed. Mentally put your toughest opponant right behind you and jump suddenly into an all-out quarter mile sprint, then drift back to tempo pace for a while and do it again. Learn to KILL.
The final half-mile of your summer runs are for finishing kick. Everyone waits until the last 300m to sprint. If your summer is filled with long hard sprint-ins, you will come into fall XC with a very unpleasant surprise for everyone at the end of the race.
When fall comes you need an arsenal of weapons with which to run XC. You can start way too fast and survive; you can sprint so hard in mid-race you destroy everyone, and you can sprint in from a long way out.
It is not just the miles you get in during the summer, it is HOW you get them in! :-) (www.gerrylindgren.com)