What should I do if I have been improperly served as the respondant in a family law case?
My friend was handed the papers (not me) and I was not even seen by the server

Well, you have them now, so you should respond. The best you can hope for with an improper service claim (and it may not be, depending) is a minor delay that will only serve to annoy everyone involved.

It may not be improper if yourr friend is over 18 and it was at your place of residence or employment depending on the state.

And what do you expect to accomplish here? You know have the summons. If you go into court and tell the judge the server didn't serve you properly, the judge may admonish the process server, but will tell you, that you got the papers and are here so what's the big deal?

Improper service is ONLY valuable when a default judgment or verdict is handed down because you did not show at the hearing. You may then be able to get the verdict overturned a new hearing scheduled. Since you did get the papers, then attend the hearing and forget about the technicality.