Okay so if you're sitting among a total group of strangers , and you want to perform for them , what do you tell them ... ? "Do you wanna see something" ?.
If all you do is card tricks,then flourishing is the easiest(not the best) way to get people interested.
But in everything else,I always start to steer the conversation slowly into whatever point or reason I have the effect to portray.And it makes it so much more natural and fluid than having to ask them and disrupt the atmosphere suddenly.
Of course,if everyone is already having a good time and there are no awkward moments,theres no reason to perform magic unless its something I really really want them to see.