Leaning forward at the ankle, while not bending at the hips is a very important part of good running posture, which helps economy and performance. Leaning forward helps better recruitment of glute muscles (hence better hip extension), and also puts you in a better position to drive the swinging knee forward. Learning to lean forward requires an element of practice and also some strength.
Resistance band running is a safe way to practice lean and also build necessary strength. It teaches the runners to lean forward while running tall, and activate glutes powerfully.
Start position: Choose a longer loop resistance band and tie one end of it to a fixed object such as a window grill or a pillar. Wrap the other end of the loop band at your hip. Move forward to create enough resistance.
Once you are in the start position, i.e. leaning forward at the ankle. Resistance from the band will help in keeping you in a comfortable lean position.
Please see the picture below (courtesy: Run Mechanics)
Resistance Band Running is a form drill & strength workout. So it is ideal to incorporate in the early part of your training cycles when you can focus on form. You can also include it in your strength training routine.