Google takes into account what you searched for before, what kind of websites you like,
your location and some 50 more variables before it presents you with the search result.
Google does this to serve you with what you most likely is looking for.
If you work with SEO you don't want search engine rankings be based on your previous searches. Instead you can depersonolize Google simply by adding another url variable "pws=0". The script below does this for you and you can also choose what Google Tld. to use.