try running every other day - so when you are running you feel fresh and go fairly fast and longer than normal.
I used 3-4 times per week training method years ago and improved my times a lot.
Sun - long run day (12-15) moderate pace - often the day after a race (I did mine at a moderate pace, but I would actually recommend going easy, easy on this one until you get used to it.
Tues - hard long tempo day (10-12) focus on going longish over going fast - make this an efficient steady state where you are holding a pace the whole way. or if you are tired from Sun shorten and go a little faster 6-8 miles
Thur - might be a little tired - so this is a shorter day 6-8 miles - I like to do a few intervals (maybe a short 3 mile tempo with 1-2 mile reps fast: as fast as you can go with 4-5 min rest)
Sat - race
For speed work I often kick the last part of each run for the last 800 or longer - this is just a progressive build up all the way to the finish.