The biggest learning is to stay within yourself. That requires figuring out what your limits feel like. When you feel like you're blowing up, back off a bit and keep going. As you continue to practice hills, especially as a beginner, your power will improve and you'll get faster but it won't get easier if you keep pushing yourself to your threshold.

Take your 24km/h speed and run it with default values through http://www.analyticcycling.com/ForcesPower_Page.html

At 0% grade, you need 65W of power to maintain 24km/h.
At 5% grade, you need 310W of power to maintain 24km/h.

I ride mostly flats myself, which means most "hills" in my area are of the 3%-4% grade at most but can be fairly long. This year I am taking on the Wisconsin Triple Crown, which has hills of a length and steepness that I simply can't find without traveling -- sustained grades of > 10% that go on for a couple of miles. The way I get up those hills -- know my threshold power, and stay within it. A power meter helps me tremendously but it's not a necessity. The suggestion of keeping a lower cadence is a good one -- you can typically sustain a slightly higher power at a lower cadence in a climb (some trainers/coaches distinguish between aerobic threshold and climbing threshold power).