One of the first questions that your partner will ask you at the beginning of a doubles match is “Do you wanna serve… or should I?”
Most of the time players just mumble something until one of them says: “Ok, you serve first!”
But really, this is a situation that should be treated seriously if you care to compete well in doubles.
I’d say that the stronger server between the two of you should serve first. In this way, if your team wins the game, that puts you in the lead and takes some of the pressure off.
On the other side, if both of you have decent serves, then you would pay a compliment to your partner by letting them serve first. That shows you have trust in them and this helps in building your team’s confidence.