There are ways to improve on speed, and then there are ways to make yourself a little quicker.
To improve speed, there are many types of runs you can do, intricate plans you can use to build up your anaerobic threshold speed and build up your endurance (intervals, tempo runs) but there are other ways you can improve time that don't involve a lot of miles and tough runs. According to The Other Mag, here are some simple tips that can shave off the seconds/minutes.
Lose Weight: Five pounds can take two minutes off the half-marathon time. For me, I could probably stand to lose about five pounds and I think once my marathon training takes off I'll get closer to 180, maybe dip into the 170s. The more miles you log, the more calories you burn so training for long runs helps shed the weight.
Wear Less: I don't necessarily agree with this as they say to ditch the fuel belt, headphones, iPhone, heavy shoes and the long-sleeve shirt around your waist. I have an iPod, not an iPhone, but I would not ditch the iPhone. It's tough for me to run without them and is something I'm adjusting to with the Lopers. I haven't worn my iPod when I go running with them. But the rest of the stuff makes sense - dragging a shirt around you on your waist only slows you down.
Sleep More: Athletes who get more sleep during training have better reaction time and speed. As little as a 20-minute nap can help performance. I'm still working on getting more sleep. Last night, for instance, I went to bed at about 9:30 or so and got up at about 4:50 this morning, although I was in bed trying to shake off the cobwebs for about a half hour. Age...
Drink Caffeine: Caffeine is supposed to increase alterness, focus but it also improves pain tolerance; they suggest drinking plain tea or coffee (NOT a mocha frappuccino) 30-60 minutes before a race or hard workout.
Limit Junk Food: Sugar can trigger hunger and can lead to weight gain. Whole-grain rice and pasta are much more beneficial than sugary foods. I tend to avoid sugar in the morning, which is when I run the most, so this isn't usually a problem. I should try and get more pasta in on the night before a long run but that doesn't always happen. Once I start logging in the double-digit miles with the Lopers, I'm going to throw in more pasta to our meal rotation.