Hills ... they are one reason why I am a fan of riding in bike shoes with recessed cleats. Easier to walk in them.
My climbing isn't very good but I decided to stick with my current gearing (53/39, 12-27) rather than swap out my $$ dura-ace groupset. It means that I will have to walk a few short steep hills above 15% but most of my routes top out at 13% and I can muscle them up with 45 seconds in the red zone.
I spend more time spun out in the 53/12 wishing I had an 11T than I spend missing gearing easier than 39/27. I'm trying out a 11-28T on another bike (shimano 105 cheap groupset) to see if I want to upgrade the good bike or if I hate the gaps. Probably still won't be able to do a 18% grade but I'm OK with that.
Steady pace and exertion level helps me. It's tempting to slack off or coast when hitting a flat spot or cresting, but you will benefit more by building a little more momentum. You can coast when you're going downhill spun out in your 50/11.
Breathing - develop a regular breathing pattern focusing on a deep exhale. The inhale will take care of itself. Shallow breathing doesn't get enough oxygen into you. Relax everything that isn't helping you propel yourself - tense arms shoulders hands feet waste energy.
Cadence of 75 would have me blowing up and overheating very quickly especially on a hill. I am a masher averaging 60rpm on most rides and 50-60 on hills. When I get below 50rpm I will alternate standing and sitting to give one set of muscles some rest while working others, but standing blows me up fast too. I sit back on the saddle, drop my heels to keep stress off the kneecaps, and use the glute muscles. I'm not getting dramatically faster on the short steep hills but have improved a lot on the long moderate hills. It's kind of fun to start out-climbing people who can do a short steep spinning little gears but don't have the aerobic fitness to maintain high cadence climbing a few miles.
As you gain experience with a particular hill, they get easier to ride just because you can home in on the most effective gearing and where to shift, where to stand, which line to follow, how to pace yourself. You'll figure out what cadence works best for you, how much torque you should be applying going into the hill.
I also had a pro fit done. The fitter moved the saddle up and back about an inch both directions. It has helped me use some natural strength and smoothed out my pedal stroke a bit.