6. Add weight training. If you've never done any weight training, you might be very surprised at how much it can improve your running speed. AND don't ignore your arms. They are the levers that help you propel the legs forward. If you are already doing weight training, consider making some changes in your workout; be sure you are doing the right exercises, and be sure you are performing them correctly. Be sure you are doing the best exercises for runners.
7. Core. Improving core strength helps you to be lighter on your feet. It will help you avoid sinking into the ground with each stride; rather you'll feel more like you're gliding over it, which is, of course, faster. Study photos of yourself when at the end of a race. You'll see that you look like your torso drops closer to the ground with each stride than it did in photos early in a race. Strengthening your core and all other muscles will help this.
8. Lose weight. Many runners can afford to lose a few pounds. Even 5 pounds will make a difference in your running speed and comfort. To investigate this, put 10 lbs of weight in a backpack and go for a run. Nothing will convince you more effectively.
9. Try some plyometric exercises. Be very careful here because these can easily get you injured and will always get you sore, at least at first. Make sure you do each exercise correctly and do them on a hard training day. Basically, plyometric exercises are explosive exercises which can certainly increase your running speed. Google plyometric exercises and runners. You'll find plenty of videos on YouTube, but be very careful, and don't do this if you are not already in peak condition. Even then, start with only one or two reps of only a couple of different ones each week, and build from there.
10. Run off road on rugged terrain at least once a week. Running through sand, hopping over roots and adjusting to varying uneven ground will require much more mental concentration, but it will also strengthen your ankles and require more balance and increase overall agility. As a result, when you run on pavement it will seem easier, and you will be stronger, enabling you to run faster. An added benefit is that it is less stressful in other ways due to the fact that it is soft surface. Therefore, it is easier on a runner's body in that way.