One easy way to make a Smiths fan is to give them The Queen is Dead. It's a pop masterpiece that works as a collection of singles as well as a unified album. There are plenty of Smiths singles collections out there, but in my view they seem somewhat "random" in their cohesiveness. Not so with The Queen is Dead; it's simply one of the greatest albums of all time. 
Not only was this the soundtrack of my high school years (along with Husker Du and the Replacements), but it's so great to go back and listen to it and find that it stands up so well after all these years. Not a bad song in the bunch (although Vicar in a Tutu was always a bit strange), with the title track, Cemetry Gates, and I Know It's Over being three of the wittiest, most brilliant songs I have ever heard. They've influenced nearly every British band that came after them (and many American bands, too) and I hope some day my (currently) 2 year-old son will be able to appreciate how much they meant to me.