It's hard to just blast out dos and don'ts without knowing the individuals and challenges involved in any particular situation.
The one universal DO of polyamory seems to be "communicate communicate communicate". Open communication makes almost any relationship better, but in newly polyamorous relationships the communications breakdowns lead to people tending to fill in the blanks with the worst they can imagine.
So I guess that's another DO. DO communicate this to your partners: "I am going to try to assume you have good intentions and think this will all go better if you both do the same for me." And then actually do that: assume good intentions until something conclusive happens that proves bad intentions.
And I guess that leads to the one DON'T that I can think of. DON'T be in a relationship with anyone who has bad intentions.