Speed work is key year round. The greatest runners in the world have amazing sprinting speed, even the distance runners. Its very important that your recruit your fast twitch muscle fibers. The best way to do speed development is to do 5-6 * 40m reps with 4 minutes rest between. Have a jog in start and spring at maximum velocity for the 40 meters. Make sure you have good running form during the sprints. The point of the 4 minutes rest is to allow the body to fully recover. I do this once a week year round. If you've never done this before don't start with 6. The first time you do this do 3, then see how your body reacts. If your sore the next day do 3 again the next week, or if you feel good do 4 the next week. Whenever you implement something new into your training take it slow and TRUST THE PROCESS. If you do this fore a couple months you will see a dramatic improvement in you top end speed, which will make you faster over fall and you'll have the speed to pass people at the end of races. Remember, this is just a supplement for strides. Doing 5-6*20 second strides 3-4 times a week is also very important for building and maintaining speed.
For summer training I'd suggest slowly building up mileage until the beginning of August where your mileage will peak before coming back down. Summer training is about building a base, RUN EASY ON YOUR EASY DAYS and stay injury free. Slowly add tempos, LT reps, and some hill reps. Run hills twice a week.