I've done a few and found them to be worth it! Sometimes I bring a table, but I usually try to use their dining table and just bring my own props. I introduce myself, give a brief blurb on my work and encourage everyone to try things on. I also bring my beads, people love to pick out their own beads for custom orders (which I rarely do on the spot but offer delivery).
If there are going to be any more then 4 guests, be sure to bring a friend to help with cash so that your free to talk to the customers.
As for incentives, I do 10% of pretax sales towards jewelry and usually throw in a pair of earrings...I'm thinking of upping this amount a little.
Some people provide an invitation with website or pics for the hostess to give out, people are more likely to go if they like what they see first. This is something I don't do yet but am thinking about it.
Check out
this link too...it's a great jewelry business how-to site!
Hth

Have fun!