The instruction how to file Writ of Mandamus (WOM) (suing government) is in this forum on the first page:
http://boards.immigration.com/showthread.php?t=194681&pp=15
How I did:
1. Find samples of WOM (could be also called Plaintiff’s complaint) on the Internet or on this forum, and compose your own. You will find names of defendants on those samples. (For N-400 there could be 2 types of WOM: before Interview, and after. If after Interview, there is a deadline for uscis to adjudicate the case: 120 days, and paragraph 1447 could be referred in WOM. If before the Interview, it seems there is not a definite deadline for uscis to adjudicate the case, and judge will decide if uscis unreasonably delayed the case. Usually, if your case is 6 mo behind processing dates, it should be enough for a judge to rule in your favor, if uscis would not schedule Interview and not adjudicate your case before 60 days deadline since all defendants receive their WOM. Attach printed web page from local uscis with the dates of processing N-400 to your WOM)
2. Find Web page of your local District court, in the district where your local uscis is. (There also could be free help for litigants without lawyers, and in the court there also could be samples of cases of WOM for N-400, which are open cases.) You will need to download from there only one form: Summon (though it wouldn’t hurt to download Local Court Rules, etc.to get familiar with).
3. Print WOM first and second copy for the court, third copy for yourself, and copy WOM plus Summon for each defendant. The first page of Summon should be addressed to one defendant, but in the place for all defendants on the first page you put "See Attachment", and attach to the Summon a page with the list of all defendants. On the first page you put 60 days for reply for defendants
4. Bring copies of WOM and Summons to the Clerk of Court. She will give you a cover page, which you will fill. Then she will stamp all papers and open the case after you pay $350, and will instruct you further, if needed. She will also assign a judge for your case, usually it is a magistrate judge. You could accept a magistrate judge, signing a form (I did), or decline, and ask for a district judge, signing another form.
5. Send WOM with Summon to all defendants using Certified mail with return receipt requested. It is called serving defendants. If you don’t know address and name of your local uscis director, you can call your District Attorney, they should provide it to you. My understanding is that the office of local District Attorney is the place where to seek answers and cooperation. Though, I put DA as a defendant in my case, perhaps only copy of WOM to DA could be enough.
Some names and addresses are here
but I'm sure the paper work is more scary than what I think. We went to my InfoPass and we were told I just cleared by FBI checks. the IO confirmed I was in place for interview. I think I will wait and see.