I especially liked this idea because you can really give it your own twist. There is so much room for creativity with the glasses, the juices, the garnishes and even the champagne! I'd love to do a holiday themed one with frozen cranberries and rosemary sprigs for garnish! Anyway, here are some of my tips.
1. As stated above, give it your own unique spin, and have fun with it!
2. Don't worry so much about the champagne quality. You're masking the flavor with juice anyway.
3. Do something fun with your glasses. We used vintage champagne glasses, but I think tumblers with fun straws could be equally as cute.
4. For it to truly be a "mimosa bar," I'd say to offer at least 3 different juices. Give your guests a good variety.
5. Make the bar accessible. Tight spaces aren't a good fit for this one. Your guests will be flocking back and forth. Make sure the area is spacey so they don't feel rushed.