It depends on why you are running the hill. Leaning forward and shortening your stride is the best way to get up it in a race, but if you are running hill repeats the best thing to do is run tall with a high knee lift and powerful hip extension.
http://home.sprynet.com/~holtrun/hill.htm
"For this session, ignore the efficient way of running hills.
Hill reps require a different action...an exaggerated running action;
though inefficient in a race, it’s perfect for our present purposes. Use
a section of about 100 meters for your first session.
After a normal warmup, you can start the first of about ten
repetitions. Run up the hill with a high knee lift and sprinters type
arm action. The legs should not be going too fast...the emphasis is on
lifting the knees higher than in normal runs...but landing softly. Land
closer to your toes than the heel of the foot...midfoot is ideal. You
will run more like a sprinter in these sessions than at any other time."