Here are some things, I believe, worked for me when training for long distance races:

• When training, always start leisurely: run your first or first 2 miles slowly (even if you training pace is 7:00 per mile there is nothing wrong in running the first mile in 9:00 pace).
• To get faster, it is very important to do one, two, or three runs at faster pace during the week. However, I do not believe that pressing the pace on the other runs during the week will be beneficiary for running faster races (I know a lot of runners that run almost every run at a steady or faster pace, but it doesn't seem to lead to good races). If you feel tired or not up to it on an easy day there is nothing wrong with running quite slowly, because that allows you to recover for your quality workouts.
• Always drink water even if you are not thirsty.
• Rest days are important; they let your minor sores heal, and they provide tapering for your hard workouts and races. Take it least one or two rest days per week; if you are totally addicted to training cross train, but give your running muscles and your back a break!
• Take rest days the day after your long runs and the day before your hardest speed workout.
• When you start a "new season" run the first 4-6 weeks only easily and increase your mileage without doing any kind of faster running (4-6 strides at the end of a run are okay). Establish a good mileage base makes you more durable for the remainder of the season.
• 1 or 2 months of hill workouts are very beneficiary early in the season. They make you a stronger runner, enhance your running economy, and prepare you for quality workouts and races in the later season.
• Very fast speedwork at a pace much much faster than race pace (e.g. 200 meters at 400 meter pace when training for a 10K) will not help you very much in improving your race times for longer distances and only gets you injured.
• Taper before important races; e.g. take two rest days in the last four days leading up to the race.
• Add diversity to your running to keep it fun! Diversity is the key to successful training, and makes running more exciting and less boring. Train at different paces, which in my opinion, is one successful ingredients of Kenyan training programs. Run different paces on different days, and change your pace within a single run (even if you do an easy run you can run "negative splits" or run the middle two miles slightly faster). Run different routes! Rotate shoes! Try new workouts from time to time, training is a continuous learning process to find out what works for you --- and what works for you changes with time. If you are interested in improving your running performance, running the same distance, on the same route, with the same pace wearing the same shoes will not get you anywhere!
• Have a off-season! Have 1-4 months per year where you run only leasurely. This gets the fun back into your running!
• Eating a lot of bread, potatoes, rice, vegetables, seafood, and fruits helps you in becoming a better runner --- I am not a strong believer in eating a lot (some is okay) of pasta: you will just gain weight (why do almost all weight loss diets exclude pasta?). Additionally, I eat significant amounts of cereal, and chicken, moderate amounts of yogurt, tofu, cakes&muffins, humus, and cheese, and very limited amount of red meat and chocolate products. I also avoid fried foods (except sometimes a eat French fries (my small sin)).
• Watch your diet and don't cheat, but schedule some "freedom days" in advance: e.g. on the day of the long run you can eat anything (I frequently eat pecan pie as a "reward" after doing a 20M long run).