Here's what I do:

Principle 1: zap the things you want to see in the world -- people who are helpful, nice, funny, cool, and who have interesting perspectives. People who respond thoughtfully when you ask something. Pretend that you'll get more of whatever behavior you zap. Pretend you're voting for the culture that will emerge here.

Principle 2: Get a feel for what the norms of the place are, and combine that with absolute value. I want people to feel it when I think they're great; but I also don't want to blow out the speakers. The amounts to accomplish this have been creeping upward, though.

Principle 3: Stay in the black. This is kind of dumb, but I wanted to see if I could do stuff that people would value after my initial buy-in. Now that I've got a large-ish stack, by the current zapping standards, I have done stuff like donate 100k sats, and give 10k when someone worth encouraging needs it. I'm pretty far in the black at this point, but I'm adjusting slowly bc I don't want to get rekt, either. Aside from book club posts, I'm generally in the red, and who knows how long the generous stackers will keep liking the book discussions.

It's a fun topic to think about. @Undisciplined did some informal calculations on zapping, maybe he'll share.