In the Christmas rush, you can charge premium prices by providing premium services.
The 3-4 weeks before hand, start experimenting with different listing formats, spread them across short BIN, long BIN and auction. You wont be able to get away with a flat percentage price increase, but you should stay aware, and increase prices as your or your competitors stock levels drop.
Edit: Don't sell at ALL 7 business days before X-mas. It's not worth it, theres a HUGE spike in people leaving negative feedback because they got their item on the 26th.
While this is good general advice, you can capitalize on other sellers who do this.
Take all of your regular listing schedules, and pause them about 8-9 days before Christmas. You do not want ANY listings going on then.
Then convert all of your listings to "FREE OVERNIGHT POST" and add the overnight shipping charge, and another 20% markup.
Advertise the next day shipping prominently in the listings and you will convert a lot of sales at a bigger margin than usual.
Stop these listings 2-3 days before Christmas, and then start up regular listings on Christmas day to capitalize on "I wanted X but only got Y"