They say that people think they're smarter than they actually are. Similarly, I think most privacy advocators think their data is more important than it actually is.
This is not to say that ditching Google is wrong; all I'm saying is you better start asking yourself "why do I not want Google to know more about me?". Unless the answer is something along the lines of "because I'm the CEO of a huge conglomerate" or "because my product is competing with one of Google's product", you're fine.
1. remove your Picasa pictures at picasa.google.com
2. since the GDrive search will not help you searching for file sizes, you'll need to install a third-party tool, I suggest WinDirStat (https://windirstat.net/)
2.1. discover the files in GDrive folder with the most size and delete the ones you'll never actually going to need (be truthful to yourself here - if you never open a 1GB in the past 5 years, why do you think you'll open it in the next 5 years?
3. Empty trash on GDrive online web application
4. search in GMail for messages larger than 1MB: "larger:1m" and delete the ones you think don't deserve staying in your folder
5. Go to GMail's trash bin and exclude them as well
6. Remove Google Chrome and install another browser, Firefox for instance, with all the needed plugins (uBlock, privacy stuff, etc)
7. Throw your Google Nest in a drawer away from you (now you won't be continuously surveilled)
8. End your Google Play subscriptions (specially GDrive)
9. Throw away your Android phone or wrap it with aluminium foil
10. Use DuckDuckGo as your main search engine (or any other web search you feel like it)
(oh, I just saw how dependent I WAS on Google!)
Still using gmail, drive, and youtube (often on private mode) and hoping that nextDnS + uBlock also shields me from having too complete a profile in Mountain View