The expression “shop around” is a mantra of personal finance journalism. Most readers know to compare deals on everything from broadband to insurance. Comparison websites make the process straightforward, but they are tools rather than a solution and using them effectively requires know-how.

Martin Lewis, of Moneysavingexpert.com, the financial website, says: “I am a fan of the sites, but I worry that people see them as a fait accompli.”

He explains that in certain areas, such as insurance, the sites do not cover the whole market and you really need to compare a decent cross-section of providers. For car cover, he says, the minimum requirement is to check Moneysupermarket.com, Confused.com and Compare- TheMarket.com in that order.

Be aware that the “quotes” from Moneysupermarket are estimates based on a short form, while those from Confused and CompareThe-Market are actual quotes. Note also that Direct Line does not appear on any comparison site, while Churchill and Privilege are listed only at TescoCompare.com.

Anyone shopping for car insurance online should also obtain quotes using all legitimate job descriptions. A lawyer could be charged less than a solicitor, for instance.

For home insurance, Mr Lewis recommends searches of Confused, Moneysupermarket, CompareTheMarket and then GoCompare.com. Also check Direct Line and Admiral, two big insurers that the sites miss.

Searching for most other products is simpler. Moneysupermarket's coverage of the loan market, for instance, is near-complete - so a visit to the one site should be adequate. But consumers should be aware that secured loans are listed alongside safer unsecured loans.

You should also be able to switch energy provider at one site. Energyhelpline.com and uSwitch.com list all suppliers. Access the former through Moneysavingexpert to earn a £15 cashback per switch. It is worth checking the website of energywatch, the independent watchdog, at www.energywatch.org.uk, to view complaints against each supplier.

Whatever service you are comparing, be aware that offerings from different companies are never alike, so the best price may not mean best value. One 8Mb broadband deal might come with extras that create added value, for example. It is worth looking closely at the small print of the cheapest deals before signing up. Mr Lewis says that complex small print makes it particularly difficult to compare credit cards, because the “cheapest” cards may carry significant disadvantages.

Once you have found the best all-round deal for a product or service, check whether you can reclaim some money through a cashback website such as TopCashBack.co.uk.

Case Study: New cover at half the price

The Rev James Steven saved £220 a year when he compared car insurance quotes at Insurance.co.uk, a new entry into the price comparison market from Lloyds TSB. The 45-year-old, who teaches theology at Trinity College, Bristol, used the site when the policy on his second car, used for longer-distance travel with his wife and three children, came up for renewal. “I would have paid £430, up from £370, if I had stayed with Norwich Union,” he says. “I switched to More Than, which charged £210.”

Mr Steven says that he went with the cheapest deal and did not research other factors, such as customer service. He adds that the site was the most user-friendly he has visited and that, as he was pleased with the More Than quote, he saw little point in shopping around further. He now plans to use comparison sites to save on utilities bills.