Sri Chinmoy: To a great extent, speed in running starts with the mind. You have to develop more imagination. Imagine that you are running fast and appreciate your speed. Then let the thrill and joy that you get from your imagination inundate you. This joy will increase your speed. You can also think of some people who really do run fast and try to identify yourself with them.
In your case, you do not have to look very far. Your husband runs much faster than you do. You have seen him running fast many times, so you can identify your legs with his. The next time you go running, as soon as you start, feel that you have borrowed his legs and from then on, whenever you want to run, feel that you will be able to use his legs.
This is all based on imagination. Of course, you can take quite a few exercises to increase your speed. Limbering and stretching exercises will help a little. But imagination plays a great role in increasing speed.