Originally Posted by MichaelW
Pedalling style can vary up a hill. I switch between seated (quite far back) spinning with a circular (not up/down) motion, and standing to get over steeper sections. In French they call this style en danse. It is dancing on the pedals, not lifting weights.
+1. Learning good spinning technique is important, but don't be afraid to stand. Standing uses different muscles than spinning, so you can often ride significantly faster for long periods of time if you alternate standing and sitting.
The key to climbing hills of any size is to just relax. If you try to power up the hills, you'll burn up your legs unless you don't have far to go.