Don't invite anyone you don't both already know.It's easy. If one of your friends hasn't met your spouse-to-be since you started dating, then how close a friend are they really?
This is not to knock friendships where you don't meet but every few years, but they can wait.
This is a bulletproof excuse against that old friend from sixth grade, or the office, or wherever...... who acts hurt that you didn't invite her(or rarely him). Tell them the rule, and they calm down right away.
(Of course, this doesn't apply to family, or anyone you don't want it to, or to guests that your guests bring with them.)