Ripped this from a bike shop web site and I sure as heck hope these tips refer to mild long hills.
If they are for steep climbs, I'd have to disagree with all of them.
here's how to conquer climbs:
# Sit tall: If you remain upright, rather than crouched over the bars,
you'll find it easier to breathe. And, if you can get more oxygen, you'll feel stronger and you
won't tire too quickly.
# Learn to stand: One of the best ways to scale hills is occasionally
standing to pedal. Although this takes a little practice to perfect, it lets you use body weight to
turn the pedals, which is easier than pushing them with muscle power alone. To do it, simply stand
up (remaining crouched slightly) and lean forward a bit. As each pedal reaches the top of the
stroke, rest your weight on it and push down to pedal. With practice this becomes fluid and the bike
rocks slightly as you shift side to side with each push. Let the slope dictate where you stand.
Rather than shifting to an easier gear, stand up on steeper sections. You'll use different muscles
and your crotch will thank you, too.
# Use an easy gear: It's always best to start hills in an easy gear and
then shift into a slightly harder one, if you feel up to it. That way, you won't burn too much
energy starting the climb and you'll be able to pace yourself to the top.