Back to the original question:
For me, I now tend to stay seated on grades up to about 12%. I have low enough gearing to keep the cadence reasonably high.

On much steeper grades, I have to stand, and then I'm just trying to keep the wheels turning. I do try to keep the bike's speed from increasing over my seated mph if possible, so I don't burn out too soon.

On longer moderate climbs ( perhaps 7% to 11%), standing is a good relief from the seated efforts. I have two methods here:
(On these hills, as I stand, I usually shift the cassette two gears harder, and see how that feels. I might go up or down from there.)

1. I'll do two to six or so pedal strokes, then coast very briefly. It might be just a one or two second coast. The idea is to keep my ,mph speed in check, and my watts more reasonable. This doesn't work that great in a group with riders right behind me, though. I'll only do it if there's a couple of bike lengths of space behind me, or I stay toward the rear of the group.
2. I got inspired by a couple of riders I know that just look effortless while standing. It's their pedal stroke, I think. Just extremely fluid so that it appears effortless. I work on this when I can. I need the correct gearing and also the correct cadence for that gear -- which also ties into mph speed vs grade. Sometimes I achieve that very smooth, efficient pedal stroke. I think I'm slightly pulling up on the upstroke, or at least unweighting the pedal. I feel that I can maintain this smooth pedaling way longer than the usual standing interval.

I also noticed this on a short gopro video clip I shot last year. Two strong riders in front of me on a very short hill, both standing. (I was going all-out to try to stay with them, workable since the climb was 10 or 15 seconds long). One was smooth and effective. The other had much more sudden body and bike movements. Very interesting.

Zwift pedal stroke efficiency
Some comments mentioned standing on Zwift. I rarely do that, I'm mostly seating when riding Zwift. But the Wahoo Kickr trainer's resistance is quite a bit different than riding outside. Outdoors, I think there can be a "micro coasting" within a pedal stroke: if I let off the power, it's strictly coasting. On the trainer, there's always resistance around the whole pedal stroke. It doesn't react to less pedal pressure that fast. I found I was putting out much less watts on the trainer compared to outdoors -- measured on the same bike, same Stages power meter. After a while, it got easier on Zwift -- I adapted. I think the better pedal stroke translates to outdoor riding -- I feel I have more power when seated at normal spinning cadences. This has to help with standing too, I think.