A good warm-up does not need to take long. It needs to raise your heart rate, loosen your hips and ankles, and remind your muscles what running feels like.
Start with three minutes of very easy jogging or brisk walking. Then do ten leg swings on each side, forward and back, holding on to a wall or a railing for balance.
Next come walking lunges: ten on each leg, with your chest tall and your back knee close to the ground. Follow them with twenty seconds each of high knees and butt kicks.
Finish with four strides. Over about eighty metres, build smoothly up to a fast but relaxed pace, then walk back to recover. Strides are the bridge between warming up and running hard.
Save the long static stretches for after the session, when your muscles are warm. Before a run they do little to protect you and can leave your legs feeling flat.