Once you know what you're up against, there are five handy steps you can take, which should keep you clear of the most common traps.
1. Start with a list - think about the meals you need to plan for, and check your cupboards. Too many people buy the same things each week, and have a pile of 10 tins of beans in the cupboard.
2. Stick to the list - make firm rules about when you can deviate and when you can't. It's fine if something you use regularly is incredibly cheap (like washing powder) but not if you spot a mulled-wine-flavoured jam and think 'that looks interesting'.
3. Take a calculator - check if you are buying the cheapest brand and the cheapest size. In some cases you'll need your calculator, and in others you'll have to take pre-packaged fruit and vegetables to the weighing scales to be sure, but don't be too embarrassed to check.
4. Consider deals carefully - they're designed to attract us, but it's important to check you need everything in a multi-buy deal, or that it actually constitutes a saving - either compared to the price of the own brand or compared to the usual price.
5. Take a receipt from last week - this is the easiest way to check the usual price of items and spot good deals and price hikes.