It's best if you pick a theme. You could try different varietals, say Merlot, Cabernet, Malbec, and Grenache and try to have everyone pick out which one is which. This is harder than you think. When we went to a tasting like this with 6 reds, only one person of 12 of us had even 3 correct! You could pick regions to compare: a French Merlot versus a Washington Merlot, for example.
I decided on a Malbecs around the world tasting. Now all I needed was the wine and the supplies.
Next, I needed to clean about 20 wine glasses. I have found the stemless glasses from World Market/Cost Plus to be the best deal. I used to own fancy, stemmed Riedels. Uh, most of those are broken now--nice crystal is fragile and dangerous to use at large wine parties--and so I switched to the stemless. The only problem is that stemmed glasses can have little wine charms on them for people to keep track of their glass. The stemless was a problem with this until I discovered these bottle writing pens that write like a charm on glass and is easy to clean off.
While you are at the wine shop or the kitchen shop buying supplies, don't forget to get some cute cocktail napkins too.
Set up your notes and glasses and be sure to have lots of pens, crackers, and drinking water handy.