My search engine echoes previous searches.

Often when I do internet searches I will tend to
get hits that echo previous searches that I have
done and previous sites that I have visited, along
with an array of parallel advertisements.

When I do searches I do not necessesarily
want to see sites that I have seen before,
or echoes of previous searches, but wish to
find new things.

What can I do to stop this?  Is it a matter
of constantly deleting cookies, or should I
do other things as well?