Christmas in Paris

To buy tickets for the opera you need to register with the site; you can do this any time. Then have your registration number and such in hand precisely when tickets go on sale. Once you are registered you might get announcements of ticket dates, but you can also find out when tickets go on sale on the official web site. To get tickets, go on line precisely when they go on sale; for me that was usually about 1:30 in the morning. The less expensive tickets go quickly so be ready to push the send when the clock ticks and then you will be in a queue till your turn comes; when it is your turn you can select tickets, see the sight line (if you don't like it you can reject those tickets and request others) and purchase. You can print them out at home if successful. I don't know when tickets for December go on sale, but I would guess in July or August; the website will show when they go on sale. they do sell out quickly in most cases. The web site is:
https://www.operadeparis.fr/en/

I am not a fan of Moulin Rouge type things but we did enjoy a sort of French folk song sing along in Paris. touristy, yeah, but mostly French tourists. You can see our evening at:
http://janettravels.wordpress.com/2011/10/09/le-vieux-belleville-non-je-ne-regrette-rien/

I did buy ballet tickets (for Copelia) at Opera Bastille on short notice around December 18, 1994, but now that booking online is easy, I try to plan ahead. They have The Nutcracker this year.