I'm pretty big into running; though Im taking a bit of time off now, I hope to run the NYC Marathon in the next 5 years. Then Boston, and hopefully the 2020 Olympic Trials.
Running is like anything else with your muscles: you have to "confuse" them. Doing the same thing everyday won't make you improve (except at that one workout, usually long slower running). Try to throw in fartlek's even if it just for 10 minutes (fartlek is Swedish for Speedplay; it could be 50s on 20s off, 60 on 30 off, or 2min on 1 min off, etc). I really love them; they are a good rust buster and can get you in good shape quickly. Another key are "tempo" runs. Running a fast, yet controlled, pace for a mid-distance (for me 5-6 miles). Maybe 1/2 to 3/4 of your longer runs, you shouldnt be breathing hard just stay relaxed. For good improvement, a long run or two (about 25% of weekly mileage, if you are running 5-6 times a week with no doubles) a week is necessary. Start slowly. Finish fast, but controlled. They have really given me some confidence in the past.
One thing that gets me is how alot of people strain when they run; watch the pro's when they race, they are flying and they don't strain/ hyperventilate. Breath deep.
Also sprinting/ running hard up hills is really beneficial to your neuromuscular coordination. I have done stuff like 3x4min segments up hill (for all 4 mins) or 5x2min. 8x1min. etc. Run hills with good arm swing, they shouldnt cross and should be "loose".
Biggest rule for improvement: Easy days easy. Hard days harder (though they will feel easier).