Do your homework.
Show up with contributions and connections long before you bring your opinion.
Save the snark for later.
Pay your dues.
Speak up about shared truths, shared principles and shared goals.
Don't blame the ref only when the call is against you.
Reflect back what you believe the other person is trying to say before you disagree with it.
If you want to persuade on the merits, avoid joining the threatening mob.
Convert six people before you try to convert sixty.
Tell true stories.