Couple of suggestions:

Exclude commonly trending words such as Google. It isn't trending if it's already huge.

I've got '[' and ']' for the last week, exclude these too.

EDIT: As a matter of fact something seems to be wrong if Google is classified as trending. There haven't been a big surge in posts about Google in the recent past. Either something is wrong, I am wrong or the algorithm is still training (e.g.: learning what is the normal rate of appearance of certain words)