Leg stabilisation is important for almost every upright human movement, be it gymnastics, martial arts, running, dance, etc. Knee and ankle stabilisation is important not just for sports, but also for general day to day activities like walking and standing. Two exercises I use to build stabilisation in my knees and ankles are the side scale and the weighted row.
For the side scale, stand with feet together either on the floor or a raised surface. Raise one leg out to the side as far as possible and hold for 10 to 15 seconds, and then repeat on the other leg.
For the weighted row, learn forward while allowing your leg to raise behind you. The rear leg should stay in line with the torso. From here, preform a row, bringing your elbow back around your spine and using your other arm as a counter balance. The added weight puts extra pressure on your stabilisation muscles.
These exercises are best performed barefoot. Most conventional runners have high sides that act as ankle stabilisers, this will prevent you from building up your own stabilisation muscles.