Another good trick is to practice standing on the flats. A simple technique is to stand at the start of your ride. Get is a big gear and just ride standing away from your starting point until you can't . Pick a landmark each time and try to ride past it. Each ride move to a farther landmark. This will also teach to glide standing which is also a good skill. lastly This doubles as a great warm up as it will get your heart rate up and warm the muscles up. Before you know it you'll wind up sitting from boredom not fatigue, and suddenly those hills will be a lot easier to get up out of the saddle on..