Very hilly round here (West Somerset/North Devon) so no choice but to climb, you do get used to it (have been cycling for 30+ yrs mind you).
Actually "enjoy" the hills nowadays (in these parts a 15 mile spin would include c4 to 5 miles climbing, (with very, very little actual flat in between) including several 16%-17% sections, 20%+ if you're feeling particularly masochistic).
Would agree with many comments posted above, especially:
Focus, look at road just ahead (remember to occasionally glance up, you don't know where some dozy whatsit has stopped the car to look at the "amazing" view!)
Breathing, keep it steady, focus required again.
Steady, relatively fast cadance for me, not exactly a spinner, but grinding would be left for the real steep climbs only (I ride 52-42 and 12-23).
In or out of the saddle is totally down to personal choice. I tend to sit in saddle most of the time, only honking if I want a quick stretch of my legs/really tough section.
If struggling but don't want to get out of saddle, sit slightly further back in saddle.
I personally find climbing (esp long climbs) easier on my own rather then in group. Very much your own speed, cadence thing for me.
Give me a long, long climb over a headwind any day of the week.
...oh, and remember to enjoy the well deserved downhill afterwards.