There are two ways; Jeff Butts thinks one is much easier, but walks you through both methods anyways.
I kind of love PetDrop Club. And by kind of, I mean I totally love PetDrop Club. This is more an idea than anything else and it works like this. “Find strangers with insecure inbound AirDrop settings, and send them kind, fluffy reminders that some people are nice, and maybe also to update their settings.” How do you do that? By sharing an image and looking for AirDrop recipients you don’t know. Or, put another way, “Reward strangers for their lack of device privacy by sending them pictures of your dog.” The site for PetClub Drop is funny, but the issue behind it is more serious. Folks who don’t lock down AirDrops to their Contacts (or turn it off) run the risk of having strangers drop all manner of unwanted stuff on their devices. There’s a PetDrop Club Google Group, too, though there’s no activity yet.
AirDrop is handy for sharing files between your devices, like your iPhone and iPad. If there are lots of other devices nearby named “iPhone” or “iPad,” just like yours, it’s time to change your iPhone’s name so you know those files are going to the right place. Luckily, that’s easy to do. Follow along to learn how.