Newsbeat has been finding out how the shops will be trying to drive sales.
Black Friday's originally a American idea linked to the Thanksgiving holiday but retailers in the UK say the annual sales day is taking off here too.
Spending will be up 22% on last year, according to Visa, which predicts that Â£360,000 will be spent every minute.
We've been speaking to retail consultants about some of the methods shops use to try to make that happen.
"An atmosphere of frenzy and anticipation" is the aim, James Logie, from Retail Management Consultants tells Newsbeat.
Many deals will be for 24 hours only, to create a sense of urgency.
Tesco's 24-hour stores began the sale at one minute past midnight and John Lewis will be revealing many of its deals then too.
"All of this appeals to our hunter instincts to go out there and get the best bargains," says Clare Rayner, a retail consultant.
But Guy Anker from moneysavingexpert.com warns: "It's classic sales pressure. Consumers and shoppers need to be on their guard.
"Just because it's on sale in one place doesn't mean that's the cheapest place to buy it.
"If you look at some of the big brands that have their own stores - even in a sale it's sometimes cheaper to buy those items at a department store or a more general store that sells any number of brands."
James says "commitment consistency" is a key tactic. This is the idea that once you've committed to buy something, you'll buy again.
We've long seen merchandise being placed by the till and there are plenty of bargains positioned there today.
Staff will be encouraging consumers to buy a matching garment, or a warranty to go with what they've already decided to buy, says Clare.
Guy adds: "What's really important is to think about what you really want and need in advance."
"High energy music can create frenzied atmosphere, stimulate the senses and create that sense of having to rush," says James.
Guy says that while the "smell of mulled wine, Christmas music, and flowers might be nice - it's all part of the sales trick to try to get you to spend.
"So try to make rational decision and not an emotional one."
Many stores will bring in extra staff - and this could be the day the Christmas hats come out.
"Staff will be on parade tomorrow, we'll see a lot more engagement than usual."
Clare says staff "really have to make this one day count".
She adds: "There's going to be very little profit margin on heavily discounted products and so they're really going to have to sell like mad to make it worth their while."
It's all about making a big impact on customers as they walk through the door, and positioning the biggest bargains where they can't possibly be missed.
"We're expecting to see big flashy signs and displays at the front of the store, with lighting to draw the eye to them," says Clare.
"Whether the shopper knows it's Black Friday or not, by the time they've walked through the door, they won't be in any doubt."
Retailers will be targeting customers by email and on their phones too.
On last year's Black Friday John Lewis says it saw online sales that were twice as big as their previous record day and sales from mobile devices were three times bigger.
With all that in mind, Gillian Guy, chief executive of charity Citizens Advice, share some advice.
"Consumer protection laws could give you the right to a refund or repair if you buy something that's faulty, is delivered late or if the product that arrives isn't what you were expecting," she says.
"Always check the terms and conditions so that if something does go wrong, you know what you can do to get it put right.
"If you buy something online, then retailers have to be up front about delivery costs and their returns policy."
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On Black Friday retailers will be aiming for a "frenzied" atmosphere - the hope being it makes you buy more.