It might sound obvious, but this really is crucial. Online retailers frequently change their pricing, with some using increasingly sophisticated algorithms to ensure they're always cheaper than their competitors.
You can be as specific or as vague as you like: if you know the exact brand, model and colour you're after, then you'll get very on-point results; while if you're at the beginning of your search and just want an idea of prices you can also plug in much looser search terms.
It's natural to get excited when you see a big saving, but sometimes the 'was' price isn't all it seems.
Some retailers use anchor pricing – showing the original selling price contrasted with a much lower 'sale' price – to trick shoppers into thinking they're getting a better deal than they really are.
For example, when we looked at products on promotion across a range of retailers in the first six months of 2020, we uncovered several items that were on promotion for more days than they weren’t.
This included two TVs at AO.com that were on offer for at least 90% of the period, and a third that spent 86% of the time on promotion. At Currys PC World, we found a Fitbit fitness tracker that had been at the anchor price less than 30% of the time.
Some products follow a predictable seasonal pattern that means you're more likely to pick up a bargain at certain times of year than others.
For example, new TV models are usually released between April and July each year. When a model has just been released it'll be at its most expensive – but if you wait until later in the year, the hype will have died down along with the prices. Or you could even wait until the new lines are released and pick up a previous-year model for a knock-down price.
Retailers also follow patterns. We found that John Lewis, for example, has than any other month, while nearly all retailers offer plenty of discounts on (at the end of November) and in the January sales.
Try Googling the name of the site you're buying from with the words 'discount code' and more often than not you'll find several websites claiming to offer codes that will save you a hefty wedge with your chosen retailer.
This can be a process of trial and error as the best codes tend to expire or only be valid for certain ranges from a retailer's website, but a discount code that works can mean a significant saving.
You simply copy the code and then paste it into the promotional code box when checking out on the website you're shopping with.
Which? research has found that it's worth using live chat to ask if the retailer can offer a discount.
Our researchers secured 20% off from Boden, 12% off from Dell and 10% off from The Perfume Shop when they tried this approach in 2017.
Some retailers are more likely to offer you a discount than others, but if you can say that you've seen the same item cheaper elsewhere, they might be more inclined to offer you money off.
Retailers often offer a discount on your first purchase if you sign up to their mailing list.
You can always unsubscribe once you've got the code and made your purchase, or set up an email account or folder specifically for promotional emails that you don't particularly want to read.
It can also be worth following your favourite brands on Facebook, Twitter and Instagram so that you're the first to find out when they're launching new sales – there might also be competitions you can enter to win free stuff.
When you're shopping online, create an account with the retailer and make sure you're signed in, then add what you like to your basket, go to the checkout, and leave the website without completing your order.
This is what marketing types call an 'abandoned cart', and will often trigger an email to be sent to you, often containing a discount code to tempt you into returning and completing your purchase.
Some retailers add quite hefty delivery charges to online orders.
If there's a branch of your chosen retailer nearby, or they offer the option to click and collect from a local pickup point such as a convenience store or other shop, it will often save a few pounds on delivery.
Signing up could get you access to bigger discounts than you’ll find elsewhere, and cashback on your purchases to boot.
Ok, so this page is all about getting the best deal – but it would be a mistake to choose a product based on price alone.
Unless you're buying something where quality genuinely doesn't matter, it's always best to choose the product first and then find the best price, rather than the other way round.
It's always worth checking reviews before you buy (just watch out for the fake ones), and then going from there.