Use those low gears and high cadence pedalling. Most people slow their cadence a bit on the hills but you should aim to reel yourself up the slopes without too much pedalling force. You only have so much power in your engine. If the slope causes you to slow down, so be it. Just pedal at a steady rate.
Toe clips may help imporove your pedalling efficiency, enabling you to apply power more smoothly over more of the pedaling circle. Clipless sytems may give you a bit more edge than toe clips, although the price is a lot higher.