If you are holding 12 mph on a one mile hill I think you are doing fine. Of course, if you wish to do better then you have to do more of it. It you want to do really well at something, say playing the piano, the only way to to play the piano a lot. Same with the bike. Go back to that hill and ride it bottom to top several times each day over weeks.

I'm asthmatic so hills or even just maintaining a hard effort on the flat, is difficult for me. Nevertheless, I press on the hills and very slowly I get better. Enough better that it is satisfying to put in a good effort. Long ago I played a wind instrument and was taught to breath with the diaphram as do opera singers and high altitude mountaineers. For me, it is of some importance to breath deliberately and thoughtfully with the diaphram. http://my.clevelandclinic.org/disord...breathing.aspx I hope the link will be helpful.

P.S. I just remembered a video on climbing in the mountains. http://www.youtube.com/watch?v=HRFNKhNhhJQ The main thing to notice in the video is how relaxed the rider is. No wasted energy. I try to keep that image in mind in my own climbing efforts.