i'd start looking around from now, to get in idea of prices etc. There will probably be deals in the run up to Christmas, but it's finding the right deal. The deals often involve a slight reduction in price (eg £20 off), but they chuck in a free game to try and make it seem like a huge bargain. OH says it's only worth it if it's a game you actually want. Otherwise, you just end up with a game you'll never play. you can often trade in the game, but even a sealed game gets you a fraction of the price. OH says a bundle with a 2nd controller is a much better deal, for when friends come around.
OH also recommends getting the disc version because you can always sell on a game when you've finished with it, whereas you can't with the digital version. Plus, the storage isn't good on the digital version, so you end up having to buy external storage, which negates any cost saving.
it's also worth looking at online retailers that give you say 10% off your first order, instead of waiting for a black friday deal.
Dont forget, to stack offers. for example, with a blue light or CSSC card, you can buy argos/currys at say 7% cheaper than their value. plus with say, Argos, you can also collect nectar points.