Clearing Cookies is definitely a good start. Cookies take essentially no effort on the trackers' part, so they are deployed a lot.

I personally usually just recommend installing the EFF's Privacy Badger [0], which eats Cookies and blocks tracking scripts all in one, while almost never breaking webpages, so while it's not perfect protection, it's a good compromise for most people.

[0] https://www.eff.org/privacybadger

Yes, that's naive, though depends on what you mean by spying. Generally speaking though, if you remove a method or source of spying that's of value, someone will find a way to get the information anyway if it's possible.