Hi Nicole,
You can use a tool such as Google Trends to compare frequency of search terms https://trends.google.com/trends/explore?geo=AU&q=%2Fm%2F09zzrh
You can enter multiple terms and compare the frequency of results, by time and location.
On page surveys can also be useful, if they are targeted at new website visitors, to find out how and/or why someone has visited your site.
Cheers,
Chris
