I you are hosting a party, the best way to get shoes-off from all the guests is to make it part of the theme. There are a number of possible themes that can incorporate shoe-lessness:
1950s Sock Hop
1960s Hippie party
Silly Slipper party- get guests to bring the silliest slippers they can find.
Ancient Greek themed pary
Ancient Egyptian themed party
If anybody can think of any others, please suggest them in the comments.