The January sales have started in France but don't despair, many bargain hunters wait until mid season to get the real deals. The winter sales, regulated by the government, began on Wednesday January 9th and last until Tuesday February 12th. These are genuine sales, with most items that might have had a sky-high retail price during the main shopping season, given good discounts. Everything is on sale in every kind of shop. These are the official sales, though you will find bargains throughout the year when you see the signs Promotion (deal) or Soldes exceptionnels (exceptional sales).
But if you miss these (and the summer sales which generally start mid June and run to the end of July), check out my Guide to bargain shopping in France.
If you're in Paris, look at the excellent advice on the Go Paris Guide to Sales Shopping