I developed really bad ITBS a few years ago, had to hop down stairs on one leg and all that. My physiotherapist used deep tissue massage (ouch!) over a few weeks, and this one stretch that helped enormously. Now i do it for 5 minutes after every run and haven't had trouble in years! you can do it any time you're warmed up, even just straight out of a hot shower. Here's how to do it (i couldn't find any pics online..so maybe get someone to read it out loud as you move into position?)
To stretch your left leg:
-lie on your right side, with your left hand flat on the ground in front of your chest. stick your right arm out behind you, so your head is on the ground.
- bend your left leg as though you're doing a quad stretch, and bend your right leg too, up to 90 degree angle (your legs should be bent so that you look like you're running, with your right leg forward).
- okay here's the hard part - grab your left leg with your right hand. Try and keep your hips and knee square. If you can't reach your leg without it hurting too much, you can use a rolled up towel or tubing wrapped around your foot and grab that with your right hand.
I hope i explained that okay. Its a bit of a pretzel but it worked really well for me. The only other thing to emphasize is good, fresh shoes. I find that I can tell exactly when my shoes are getting old because my knee starts to hurt by then end of a long run.