Consumers should visit more than one price comparison site before switching energy suppliers.
The advice from the Competition and Markets Authority (CMA) follows a year-long study into those sites and other apps in various sectors.
Companies often pay to appear on the lists of comparison sites, which may receive commission when consumers switch providers.
They may also pay to be pushed up the rankings and not all suppliers appear on the sites.
The CMA also suggests looking for sites that show reviews and product features and visiting sites of suppliers that are not included on the comparison website.
It has laid down ground rules for all sites on issues such as communicating how they plan to use people’s personal data and clearly displaying important information like price and product description.
The competition watchdog also recommends all sites to be clear about how they make money, how many deals they’re displaying and the order of results.
It will be taking enforcement action if it suspects the law may have been broken.
Andrea Coscelli, CMA Chief Executive said: “Our study has found that most people in the UK have used a comparison site at least once so it is vital that everyone gets the benefits they deserve.
“But we have also found that improvements are needed to help people get even better deals. We have set out ground rules for how sites should behave as well as being clear on how regulators can ensure people have a better experience online.”