Start with easy walking or jogging to warm your muscles and increase the blood and lymphatic flow. Walk easy for one minute, then walk briskly (on the edge of running) for one to two minutes before you start to run.
If you have any niggling areas that are giving you trouble (like IT band or calf tightness), do some self-massage with light, short strokes. Again, you're not trying to release the tension in the targeted spot but rather warm it up. If you don't have any tight spots, skip this step.
The key for runners is to target the muscle groups used for running. You want to warm up with flexion and extension of the legs, and lateral movements, especially before harder effort runs or races. Warming up the hips, for instance is key because that's where the hip flexors, psoas, and quads and hamstrings come in together.
A note to remember: Avoid static stretching i.e. holding stretches for a period of time. Although it may seem counter intuitive, the goal of a running warm up is to warm the muscle, increase circulation and prepare the muscles to be on point to fire. Static stretching targets the muscle to relax, and impairs their ability to store energy. That's not to say static stretching is bad, it's not. But it doesn't belong in a runner's warmup routine.
Hip Circles: Standing with your feet hip width apart with your hands on your hips, rotate your hips in circles in a clockwise and then counterclockwise pattern ten times each direction.
Walking Lunges: Step forward with a long stride and drop your back leg towards the ground. Focus on keeping your front knee over your ankle and perform it in a slow and flowing motion.
Butt Kicks: Walk forward slowly while kicking your heels in towards your glutes for a total of 20 kicks (10 per leg).
Monster Walk: With your torso tall, walk forward while lifting your legs straight in front of you. Do it 10 times on each side.
Leg Swings: While holding onto something stable, swing one leg to your side and then back and across your torso. Perform the move 10 times each side.