Japan Travel Fixes
How do omikuji fortune slips work?
You usually shake a box to draw a numbered stick, then take the matching paper slip, or select one directly. Fortunes range from "great blessing" down through "blessing," "middle blessing," and "small blessing," to "curse." If the result isn't good, it's common to tie it up at the site before leaving rather than take it home.
The exact ranking order varies a little between shrines and temples, but "great blessing" being the best result is consistent everywhere.
Technically you're allowed to keep a bad fortune, but the widespread custom is to tie it to a designated rack on the grounds, symbolically leaving the bad luck behind.