Browser cookies are useful in some instances; unpleasant in others. While they can save you from having to go through a complicated authentication process whenever you're trying to access your favourite sites, they can also store data on what you've done on a particular website -- which can then be used to serve you more "relevant" advertising at a future point.
To address this, pick up the extension Cookie AutoDelete for Chrome or Firefox. It's a useful way to see just how many cookies any website is dropping into the background of your browser. More importantly, you can whitelist cookies for the sites you care about - like your favourite social network, for example - and automatically delete all cookies for other sites whenever you close the site's tab (or close your browser).
As Android Central describes:
"You can export and import whitelists and greylists, see how many cookies a site is using via the icon, clean all cookies from the same domain (like facebook.com), and clean things by hand through the pop-out extension window. This is the best extension ever and using it is more fun than Pokémon Go. Maybe that's just me."
While we'd probably rather go outside and play with Charmander than sit inside, meticulously scrubbing away our browser cookies, Cookie AutoDelete is a great way to gain a little more control over the information websites can use against you. If the extension had a way to more specifically show you what's in the different cookies each site is using, that would be even better, but it's still a pretty compelling privacy tool without it.