The brands I look out for during this period are usually Metamorphose, h.Naoto Gramm and Innocent World. For a new lolita who's on a budget but wants to get some good brand pieces, this period can be especially fortuitous.
Earlier in January this year after a rather disastrous try at the h.Naoto sale (the website crashed on me the minute the sale went online. When I did get in, items were being sold out even as I browsed =X), I turned to Metamorphose. I did see a few items that I really like but I wasn't sure yet and didn't click to buy immediately.
See, here's a little tip for Metamorphose sales: if you're willing to take a chance, Metamorphose usually further reduces the prices of their still unsold sale items after 2 or 3 weeks. It's a risk but it can pay off as prices can go down to as much as 50%.
For me, I took that chance and waited for the second reduction and got this:
The solid bustle pinafore jsk in black which went down to 11400yen after the second reduction.
Which will look like this when I take it out of the plastic pack, lol
I also participated in the Innocent World sale (still-ongoing!) and bought a jsk and some socks. For Innocent World, they rarely do further reductions for their sales so if you see something you like, get it immediately. Especially if it says 'few remaining' on the quantity. As this means they probably only got one or two pieces left!