5. Don't bully or belittle. One behavior I have seen again and again in unsuccessful conversations about open relationships is one partner treating the other as though he/she is unenlightened, uptight, brainwashed, jealous ... pick your patronizing insult. The results of this approach are no better than when the partner who is against an open relationship accuses the other of being slutty, immature, immoral or worse.
Relationships are about emotional needs as well as shared values. Even if the idea of monogamy no longer makes sense to you intellectually, remember that decisions about relationships and love are deeply emotional. They don't always rely on the rational.
Our relationships are not just socio/political exercises, they must be uniquely shaped by the humans in them. Be respectful of your partner's stance and honor the emotions and vulnerability at play.
6. Expect a long conversation. Look at this as a shared exploration. The two of you cannot figure out how you feel or what will work for you in one sitting. This will take time to develop, a series of conversations, starts and stops, re-evaluating, questioning and even back-tracking. All of this is okay. In fact, it is the basis of an honest, alive and growing relationship.