My secret on hills is Belly Breathing. Use your stomach muscles to help pull down your diaphram to get the maximum amount of air into your lungs. Having enough air is the secret, you'll find that your legs are probably strong enough to get you up any hill, but that you just plain run out of air.
It's well detailed in the book
Bicycling Bliss by Portia Masterson. Check it out at the link.