Well, it all depends.

As a beginner, your primary goal may be simply to get to the top of a hill and down the other side without keeling over, having to stop, etc. In that case, I think good technique is mostly about figuring out how to tackle hills without going too hard too early and exhausting yourself. Where shifting is concerned, much is made about spinning a low gear, but as CDR points out this loads your cardiovascular system more and you will probably find it more helpful on longer hills to switch between a higher cadence while seated and a lower cadence while standing. But what's most important is limiting your initial effort to something you can sustain. Again, CDR explained this: if you are on a slope of a certain steepness and going a certain speed, you are producing the same power regardless of what gear you a using. The only way to save energy, if you are going harder than you can sustain, is to slow down. I would recommend starting a longish hill at a pace that feels too easy. You will likely find, by the midway point, that it doesn't feel too easy after all.

When you get stronger and more experienced, you may find that you can definitely get over all the hills that you come upon, and now you want to get up them as quickly as possible. Here, I think that discussion of sitting and spinning vs. standing is even less relevant. No matter what you do, it's going to be hard, and you'll be switching back and forth depending upon slope, how your legs feel and so on. It really is all down to pacing, when it comes to getting up a hill in the shortest amount of time. And the right pacing really does take experience to learn, but once again, it's about not going too hard too early and blowing up halfway up the climb.