My son has just learned a new trick. We're in Super Target and he's looking at some small sets of Bionicle masks. He asks, "How many can I get?" Before I know it I've said, "You can get one."
Notice he did not ask, "Can I get any?" He has formulated the question so that he is practically guaranteed an answer he'll like.
I think I have been the transmitter of this strategy. Lately, I've been asking questions like, "How many hot dogs do you want for dinner?" instead of "Do you want hot dogs for dinner?"
I learned this from my boss, who has taught me that it's easier for people to say "yes" than "no" if you give them a choice they can affirm.
At first, I was worried that this would feel manipulative, but as it turns out, it just makes both people feel good about the outcome.