To find the unit rate of beads per bracelet, we need to divide the total number of beads by the number of bracelets.
Ruby has 156 beads and is making bracelets for 12 friends:
\[ \text{Unit rate} = \frac{\text{Total beads}}{\text{Number of friends}} = \frac{156 \text{ beads}}{12 \text{ friends}} = 13 \text{ beads per friend} \]
Therefore, the unit rate of beads per bracelet is 13 beads.