Who serves first in a doubles match can be the difference between winning and losing. The stronger server on your team always should start serving. Lead with your strength. If the better server goes first, he will serve twice in the first six games of the set, the weaker server only once.
Consider what could well happen if you start with your weaker server and the other team opens with its stronger server. If the better servers on both teams win their serves, and the weaker servers lose theirs, your team will lose the set 6-4.
Put your better server first and you seldom will face set point with your weaker server on the line.
Remember too - which many weekend doubles players don't - that you can change the order of service with the beginning of any new set. You want to lead with your stronger server at the start of every set.