What is that saying? "That which doesn't kill you makes stronger?" For sure on hills. I ride regularly with a group in Southern California, so there are lots of hills to ride. The best way to get better at climbing is to just keeping looking for opportunities to do it. Some things that have helped me:

On long hills, find a good gear and steady rhythm. Hands on the tops of the handle bars in order to keep your lungs open. Pedal in circles. Focus on breathing and turning over those cranks.

The best advice I was given on those long climbs is to find a comfortable pace, so as not to blow out at the bottom. Once you get to the top third or so of the hill, pick up your place, put it in a slighter harder gear and push for the top ... "up and over."

I used to get frustrated at those cyclists who go zipping by me at the bottom, until I learned that if I keep the same pace at the beginning, I usually am able to steadily gain ground on them and pass them when they're spent!