One habit I try to overcome on hill climbing is that when I don't pay attention, I begin to synch my breathing along with my pedal strokes- one whole in/out short breath per stroke. This is no good! When I catch myself doing that I stop it and start breathing more relaxed and deeply and slowly. When i do that it winds up being about 1/3 less the number of breaths, but much deeper breaths, and I feel like I'm getting more oxygen...my heart slows down and I relax more.
Pay attention to your breathing cadence and avoid having it synch to your pedaling.