What are the best ways to feed advertisers incorrect data? If they already have valid data on who I am and what I do, what could make them overwrite this knowledge?

I've used adNauseam (only on FF, Chrome booted it from their store) and TrackMeNot. AdNauseam blocks ads, but also virtually "clicks" on them to make it look like you are interested in every ad served to you, filling your data profile with noise (in theory). In practice the jury is out; some ad tech insiders have suggested they can really easily tell when this is happening, and it ultimately serves as a way to MORE easily identify you by providing bits of entropy.

TrackMeNot does a similar thing with google/bing/yahoo, submitting random popular queries to search engines in the background. It even emulates "bursty" search behavior, where you might not input a query for an hour, and then do 5+ queries in 5 minutes. I use this and have actually seen its effects, my "filter bubble" is much less tech-oriented and this effects auto-complete, result ordering and even the news articles I get in my Google Now shelf on my android phone.

https://addons.mozilla.org/en-US/firefox/addon/adnauseam/

http://trackmenot.io/